CN110860696A - Method for preparing nano aluminum powder - Google Patents
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- CN110860696A CN110860696A CN201810982539.XA CN201810982539A CN110860696A CN 110860696 A CN110860696 A CN 110860696A CN 201810982539 A CN201810982539 A CN 201810982539A CN 110860696 A CN110860696 A CN 110860696A
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F9/00—Making metallic powder or suspensions thereof
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- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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Abstract
The invention provides a method for preparing nano aluminum powder, which is characterized in that raw materials of aluminum salt are uniformly mixed in a solvent, and the nano aluminum powder is prepared under the condition of a protective agent triphenylphosphine oxide. By controlling the reaction conditions, nano aluminum powder with different particle sizes can be obtained, and the obtained nano aluminum powder is characterized by using methods such as X-ray diffraction, infrared spectroscopy, particle size analysis, thermogravimetric analysis and the like. The method provided by the invention has the advantages of simple operation, simple required raw materials, high yield and small average particle size of the prepared nano aluminum powder.
Description
Technical Field
The invention relates to a separation technology of nano-powder, in particular to a method for preparing nano-aluminum powder.
Background
Nanomaterials exhibit many significant effects, such as small-scale effects, surface-to-interface effects, quantum-scale effects, and macroscopic quantum tunneling effects, due to their size between atomic clusters and macroscopic objects. Therefore, the material has different properties from common materials with the same composition, has important application in the fields of chemistry, mechanics, magnetics, electrics, thermology and the like, and brings great economic and social benefits to various domestic industries.
The nano metal powder has the advantages of high combustion heat, high activity and the like and is utilized in the solid propellant, wherein the nano aluminum powder is a commonly used additive. The nano aluminum powder is added into the solid propellant by less than one percent, so that the combustion heat of the propellant can be doubled, the specific impulse in the propellant can be improved by nearly 1.5 times, and the combustion efficiency of the solid propellant can be obviously improved. The addition of the aluminum powder is mainly used for improving the specific impulse and combustion heat of the solid propellant, but when the nano-scale aluminum powder and the common aluminum powder are heated on the surface of the propellant, the larger-particle aluminum powder is firstly melted and condensed to form 'agglomerates' before combustion, so that the aluminum powder is insufficiently combusted, and the improvement of the combustion speed of the propellant is not facilitated. Meanwhile, infrared signals can be increased when large-particle aluminum powder is combusted; two-phase flow loss of the solid rocket engine is caused, so that the specific impulse of the engine is reduced; and the plume formed affects the guidance signal. Compared with the conventional aluminum powder, the nano aluminum powder has quick combustion and large heat release, so that the combustion heat of the fuel can be improved by about 1 time by adding 1 mass percent of ultrafine aluminum or nickel particles into a solid fuel propellant. Although the volume fraction of the passivating oxide of the nano-aluminum powder is much higher than that of the ordinary aluminum powder, the heat flux to the unburned propellant is still larger than that of the ordinary aluminum particles. The nano aluminum powder has larger specific surface area and specific surface energy, so that the nano aluminum powder also has stronger activity and reaction capability; the nano aluminum powder can quickly absorb a large amount of heat to reach the activation temperature, so that the ignition delay time of the nano aluminum powder is much shorter than that of common particles and can reach 12 orders of magnitude.
In addition, scholars at home and abroad carry out different coating modifications on the surface of the nano aluminum powder, which mainly comprise: oxide wrapping, metal wrapping, carbon wrapping, organic wrapping and the like. The measures can well isolate the nano aluminum powder from air, and the great advantage of the nano aluminum is better exerted. Al-Fe prepared by Lawrence Levermore national laboratory through sol-gel method2O3Nanocomposites, which exhibit greater sensitivity to combustion and also exhibit less sensitivity to spark and friction testing than conventional thermites.
Therefore, many fields of nano aluminum materials have been studied, including four aspects of preparation, macro physical properties, microstructure and application of nano aluminum powder particles, and the most important aspect at present is the preparation method of nano aluminum powder particles.
The method for preparing the nano aluminum mainly comprises an evaporation condensation method, a linear explosion method, a mechanochemical method, a pulse laser ablation method, an arc discharge method, a solution chemical method and the like. In the aspect of application, nano aluminum has important application value, however, in the aspect of the current preparation method, the development of nano aluminum in the aspect of application is restricted by expensive cost and smaller yield.
The common solution chemical method for preparing the nano aluminum has the defects that the product is easy to oxidize, easy to agglomerate, high in cost, low in yield, easy to coat by-product LiCl impurities and the like in the preparation process.
Therefore, the development of a novel preparation method of the nano aluminum powder with low cost, large yield and small particle size, which is not easy to agglomerate, has extremely important significance.
Disclosure of Invention
In order to solve the above problems, the present inventors have conducted intensive studies and, as a result, have found that: adding raw material lithium aluminum hydride into anisole by using a solution chemical method for ultrasonic dissolution; adding raw material aluminum trichloride into anisole, dissolving by ultrasonic, mixing uniformly in anisole, and reacting under the condition of protective agent triphenylphosphine oxide to prepare nano aluminum powder. By controlling the reaction conditions, nano aluminum powder with different particle sizes can be obtained, and the nano aluminum powder is characterized by methods such as X-ray diffraction, infrared spectroscopy, particle size analysis, thermogravimetric analysis and the like, thereby completing the invention.
The invention aims to provide a method for preparing nano aluminum powder, which comprises the following steps:
step 2, dispersing an aluminum salt II in a solvent II;
step 3, reacting the system in the step 2 with the system in the step 1;
and 4, carrying out post-treatment to obtain the nano aluminum powder.
Wherein, in the step 1,
the aluminum salt I is an aluminum salt soluble in water or an organic solvent, preferably a single aluminum salt or a composite salt of aluminum and an alkali metal, and more preferably lithium aluminum hydride;
the solvent I is a polar organic solvent, preferably an ether solvent, such as anisole, phenetole, diphenyl ether, more preferably anisole;
in the step 1, the mixing manner includes stirring or ultrasonic oscillation, preferably ultrasonic oscillation, so that the mixing is uniform.
Wherein, in the step 1, a protective agent is also added, and the protective agent is an organic phosphine oxide compound which comprises alkyl phosphine oxide, aryl phosphine oxide and alkyl aryl phosphine oxide, and is preferably aryl phosphine oxide.
Wherein the protective agent is triphenylphosphine oxide.
In the step 2, the aluminum salt II is an aluminum salt soluble in water or an organic solvent, preferably a single aluminum salt or a composite salt of aluminum and an alkali metal, and more preferably aluminum trichloride; and/or
The solvent II is the same as the solvent I.
In the step 3, under the protection of inert gas, dropwise adding the aluminum salt II solution mixed in the step 2 into the mixed solution of the system in the step 1, controlling the reaction temperature and the dropwise adding time during dropwise adding, continuing to react until the reaction is complete, stopping heating, cooling to room temperature, and/or
The reaction temperature during dripping is 140-170 ℃.
Wherein the molar ratio of the aluminum salt II to the protective agent is 1: (2-25), preferably 1: (3-20).
In the step 4, the post-treatment comprises centrifuging the reaction solution, washing and centrifuging the solid by using a solvent III after the centrifugation is finished, then washing by using a solvent IV, and then drying to obtain nano aluminum powder; and/or
The solvent III is absolute ethyl alcohol, and the solvent IV is acetone.
The nano aluminum powder prepared by the method has a small average particle size of preferably 20-60 nm, and more preferably, the melting peak of the prepared nano aluminum powder is lower than that of the conventional aluminum material, such as about 40 ℃ lower than that of the conventional aluminum material, and particularly, the melting peak of the nano aluminum powder is about 622 ℃ as shown by TG-DSC analysis.
According to the method for preparing the nano aluminum powder and the prepared nano aluminum powder, the following beneficial effects are achieved:
(1) the method provided by the invention is simple to operate and has few byproducts;
(2) the method provided by the invention has less loss of the nano aluminum powder in the preparation process;
(3) the method provided by the invention has good preparation and separation effects, is not easy to agglomerate, and the prepared and separated nano aluminum powder has small particle size, and the average particle size is less than 50 nm;
(4) the melting point of the nano aluminum powder prepared by the method provided by the invention is much lower than that of the conventional aluminum material, for example, the melting point is about 40 ℃ lower, and the melting peak is about 622 ℃.
Drawings
Fig. 1.1 and fig. 1.2 respectively show the XRD spectrum of the obtained nano aluminum powder and the standard XRD spectrum of the aluminum powder;
FIG. 2 is a line graph showing the average particle size of the nano-aluminum powder according to the Sheer's formula;
FIG. 3 shows the infrared spectra of the nano aluminum powder obtained in examples 1 to 5;
fig. 4 shows a thermogravimetric analysis spectrum of the nano aluminum powder obtained in example 3.
Detailed Description
The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.
The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
The present invention is described in detail below.
The method adopts a solution chemical reaction method to prepare the nano aluminum powder, and has the advantages of simple and easy operation and short operation period. The basic principle is to select one or more proper soluble metal salts, and prepare the soluble metal salts into solution according to the prepared material components, so that each element is in an ion or molecular state. The solution is a proper solvent, metal ions are uniformly precipitated through a series of operations, and finally the product is washed and separated to prepare the nano powder.
The inventor tries to prepare the nano aluminum powder by using a proper solvent anisole and a protective agent triphenylphosphine oxide so as to prepare the nano aluminum powder which has small average particle size and is not easy to agglomerate.
The inventors surprisingly found that the nano aluminum powder obtained by the method for preparing nano aluminum powder of the present invention has a small average particle size, preferably 20 to 60nm, more preferably 25 to 50nm, and a melting peak about 40 ℃ lower than that of the conventional aluminum material, especially about 622 ℃.
According to the invention, the method for preparing the nano aluminum powder comprises the following steps:
step 2, dispersing an aluminum salt II in a solvent II;
step 3, reacting the system in the step 2 with the system in the step 1;
and 4, carrying out post-treatment to obtain the nano aluminum powder.
Wherein the content of the first and second substances,
the aluminum salt I is an aluminum salt soluble in water or an organic solvent, preferably a single aluminum salt or a composite salt of aluminum and an alkali metal, and more preferably lithium aluminum hydride;
the solvent I is a polar organic solvent, preferably an ether solvent such as anisole, phenetole, diphenyl ether, more preferably anisole.
In step 1, a protecting agent is also added, wherein the protecting agent is an organic phosphine oxide compound and comprises alkyl phosphine oxide, aryl phosphine oxide and alkyl aryl phosphine oxide, preferably aryl phosphine oxide and more preferably triphenyl phosphine oxide.
The dosage ratio of the aluminum salt I to the solvent I is 0.2 g: (20-60) mL.
In step 1, the mixing uniformly comprises stirring or ultrasonic oscillation, preferably ultrasonic oscillation, so that the mixing is uniform.
In the step 1, the mixing mode comprises stirring or ultrasonic oscillation, and the stirring can be electromagnetic stirring or mechanical stirring; and (3) ultrasonic oscillation mixing, namely placing the reaction container in the step (1) into an ultrasonic machine for ultrasonic oscillation, and using an ultrasonic oscillation method to assist aluminum salt to disperse, wherein the ultrasonic oscillation time is 10 min-1 h.
Lithium aluminum hydride (LiAlH)4) Can exist stably in dry air at normal temperature. Is vulnerable to moisture. React violently in the presence of water and alcohol. Solubility of lithium aluminum hydride: insoluble in hydrocarbons, soluble in diethyl ether, tetrahydrofuran, dimethylcellosolve, slightly soluble in n-butyl ether, insoluble or very slightly soluble in hydrocarbons and dioxane.
Anisole, formula C7H8O, with the relative molecular weight of 108.13, is colorless liquid, has the melting point of-37 to-38 ℃, the boiling point of 155 ℃, the relative density of 0.9980 to 1.0010 and the refractive index of 1.5165 to 1.5175. For organic synthesis, and also as solvents, fragrances and insect repellents. Insoluble in water, and soluble in ethanol, diethyl ether, etc.
Step 2, dispersing an aluminum salt II in a solvent II;
in the step 2, the aluminum salt II is an aluminum salt soluble in water or an organic solvent, preferably a single aluminum salt or a composite salt of aluminum and an alkali metal, and more preferably aluminum trichloride; and/or
The solvent II is the same as the solvent I.
Aluminium trichloride (AlCl)3) I.e. aluminum chloride, which is a colorless transparent crystal or a white, slightly yellowish crystalline powder. The vapour of aluminium chloride, either dissolved in a non-polar solvent or in the molten state, is present as covalently dimerised molecules. Aluminum chloride is soluble in water and many organic solvents. The aqueous solution is acidic. In the presence of aromatic hydrocarbons, aluminum chloride and aluminum are mixed to synthesize bis (aromatic hydrocarbon) metal complexes.
In the invention, aluminum salt II is dispersed in solvent II, and optionally stirred or ultrasonically oscillated, wherein the stirring can be electromagnetic stirring or mechanical stirring; preferably, ultrasonic oscillation is used, and the aluminum salt is assisted to disperse by using the ultrasonic oscillation method, wherein the ultrasonic oscillation time is 10min to 1 hour.
The inventor finds that the aluminum salt II is dispersed in the solvent by using the ultrasonic oscillation method, so that the finally obtained nano aluminum powder has smaller particle size and is less prone to agglomeration.
The preparation method of the nano aluminum used in the invention is a solution chemical method. The basic principle of the solution chemical reaction method is to select one or more appropriate soluble metal salts, and prepare the solution according to the prepared material components, so that each element is in an ion or molecular state. The solution is prepared by selecting proper solvent, then carrying out a series of operations to precipitate metal ions evenly, and finally washing and separating the product to prepare the nano powder. The solution chemical method for preparing the nano aluminum is to reduce aluminum salt in a solvent system to realize the synthesis of the nano aluminum, and the reaction equation is AlCl3+3LiAlH4＝4Al+3LiCl+6H2。
The inventor finds that the main raw materials of the reaction are anhydrous aluminum chloride and lithium aluminum hydride, and the melting points of the anhydrous aluminum chloride and the lithium aluminum hydride are 180 ℃ and 140 ℃ respectively, so that the organic solvent with the boiling point higher than 140 ℃ and low toxicity is selected as far as possible, and the anisole is selected as the reaction solvent, so that the anhydrous aluminum chloride and the lithium aluminum hydride have better solubility, the lithium aluminum hydride is in a liquid state during the reaction, and the full reaction with the anhydrous aluminum chloride is facilitated.
The inventor finds that the nano aluminum is very active, so that oxygen in the air is easy to rapidly change into aluminum oxide. Therefore, the use of a suitable protective agent is very important for the chemical preparation of nano aluminum powder.
The present inventors found that P atoms are easily coordinately bound to metals, and that the movement of nano aluminum particles is prevented or slowed down because the surface of Al atoms is coordinately bound to phosphorus in triphenylphosphine oxide (TPPO). Meanwhile, triphenylphosphine oxide has the effects of preventing aluminum particles from aggregating and protecting nano aluminum from being oxidized, and the agglomeration of nano aluminum can be prevented due to the steric hindrance caused by triphenylphosphine oxide molecules on the surface of Al, so that the generated Al has small particle size and high stability. The triphenylphosphine oxide is used as a protective agent in the reaction process, so that the generated nano aluminum powder can be effectively prevented from being rapidly oxidized in the air, and the nano aluminum powder can be formed. In addition, the reaction raw materials are isolated from water and oxygen, so a protective gas must be used in the reaction process.
According to the reaction equation of the lithium aluminum hydride and the aluminum trichloride, the molar ratio of the lithium aluminum hydride to the aluminum trichloride is (2-6): 1.
The inventor finds that the dosage of the triphenylphosphine oxide serving as the protective agent is important for the preparation process of the nano aluminum powder, and the dosage of the triphenylphosphine oxide influences the particle size of the nano aluminum powder. The molar ratio of triphenylphosphine oxide to aluminum trichloride in the invention is (2-25): 1, preferably 1: (3-20), such as 1:5, 1:7.5, 1:10, 1:12.5, 1: 15.
Step 3, reacting the system in the step 2 with the system in the step 1;
in the step 3, under the protection of inert gas, dropwise adding the aluminum salt II solution mixed in the step 2 into the mixed solution of the system in the step 1, controlling the reaction temperature and the dropwise adding time during dropwise adding, continuing to react until the reaction is complete, stopping heating, cooling to room temperature, and/or
The reaction temperature during dripping is 140-170 ℃.
Due to LiAlH4And AlCl3The reaction is easy to occur in water and oxygen, so the water-free and oxygen-free environment is always kept in the weighing process, the dispersing process and the reaction process.
The reaction temperature during dripping is 140-170 ℃, the dripping time is 15 min-1 h, and the continuous reaction time is 10 min-1 h.
The inventor finds that at 140-170 ℃, the prepared nano aluminum particles are gradually reduced along with the increase of temperature. The reaction rate increases with increasing temperature, and higher reaction rates favor maintaining a higher degree of supersaturation during the nucleation phase, resulting in the formation of more nuclei, which results in a relatively smaller final growth size of the individual particles. Since anisole has a boiling point of 155 ℃, the temperature is at most 154 ℃ when the solvent is anisole.
In the invention, the ultrasonic oscillation is preferably carried out for 15-30 min after the heating is stopped, and the inventor finds that the ultrasonic oscillation method is used for assisting the aluminum salt to disperse in the solvent, so that the generated nano aluminum powder can be effectively broken up and uniformly dispersed in the dispersing agent, the longer the ultrasonic oscillation time is, the better the dispersing effect is, but the longer the ultrasonic oscillation time is, the solvent is volatilized in a large amount, and the dispersing effect is reduced, so the ultrasonic oscillation method is preferably used for assisting the nano aluminum powder to disperse.
And 4, carrying out post-treatment to obtain the nano aluminum powder.
In the step 4, the post-treatment comprises the steps of centrifuging the reaction liquid, washing and centrifuging the solid by using a solvent III after the centrifugation is finished, then washing by using a solvent IV, and then drying to obtain nano aluminum powder; and/or
The solvent III is absolute ethyl alcohol, and the solvent IV is acetone.
The present inventors have found that LiCl, a reaction by-product, and unreacted triphenylphosphine oxide (TPPO) can be removed well by washing with absolute ethanol and centrifuging in the post-treatment.
The inventors have also found that the dried product is less likely to cake when post-treated by washing with acetone.
Wait for the final centrifuged product to dry. The drying method is not limited, and vacuum drying is preferable.
The nano aluminum powder prepared by the method has the advantages that,
the XRD peak positions of 38.3 degrees, 44.5 degrees, 65.2 degrees, 78.1 degrees and 82.4 degrees have characteristic diffraction peaks;
the aluminum powder has a nano-grade particle size, for example, the particle size range of the obtained aluminum powder is 20-60 nm, preferably 25-50 nm;
the nano aluminum powder prepared according to the invention has special thermal effect, for example, the melting characteristic is obviously different from that of the conventional aluminum material, and the melting peak of the nano aluminum powder prepared according to the invention is obviously lower than the melting point of the conventional aluminum material, for example, even about 40 ℃ lower than that of the conventional aluminum material, and the melting peak of the nano aluminum powder is preferably about 622 ℃ as shown by TG-DSC analysis results.
Examples
Example 1
A clean 250mL four-mouth flask, four glass plugs, a stirrer and a 25mL constant pressure dropping funnel are taken, vaseline is slightly smeared on the glass plugs to prevent the solution from leaking, then the four-mouth flask, the constant pressure dropping funnel and the glass plugs are sequentially placed into a vacuum glove box according to the right steps, and the glass plugs are not plugged on the four-mouth flask during vacuumizing so as to prevent the flask from cracking. 2.82g of triphenylphosphine oxide (TPPO) (triphenylphosphine with AlCl) are weighed out on an electronic balance using a weighing paper3In a 5:1) amount of 40mL of anisole, pouring the anisole into a four-necked flask for mixing while placing a stirrer, and weighing 0.23g of LiAlH4Adding into a four-neck flask, performing ultrasonic treatment in an ultrasonic cleaning machine for 30min, and taking out after the medicine is almost dissolved in the solvent;
another 0.27g of anhydrous AlCl is taken in a vacuum glove box3Simultaneously measuring 10mL of anisole by using a measuring cylinder, pouring the anisole into a dropping funnel for mixing, and ultrasonically oscillating for 20min until the AlCl is anhydrous3Dissolving completely;
taking the four-mouth flask out of a fume hood for operation, opening the air suction function of the fume hood, firstly pulling out a glass plug to introduce argon, then quickly connecting the flask with a condenser pipe and placing the flask on an intelligent magnetic stirrer for heating, stirring (the rotating speed is 650r/min), inserting a thermometer to heat to 154 ℃, opening a piston of a constant-pressure dropping funnel, enabling liquid in the constant-pressure dropping funnel to drop into the four-mouth flask drop by drop, controlling the dropping speed to be dropped in 25 minutes, continuing to react for 30 minutes until the solution is completely changed into ash, stopping heating, ultrasonically oscillating for 30 minutes, cooling to room temperature, and preparing for post-treatment;
pouring the solution in the four-mouth flask into a centrifuge tube, putting the centrifuge tube into a centrifuge, centrifuging at a rotation speed of 5000r/min for 6min, washing and centrifuging with absolute ethyl alcohol for 3 times respectively, and washing with acetone once. Drying in a vacuum drying oven (35 deg.C) for 1.5h, and collecting the product after completely drying. The obtained product nano aluminum powder is marked as No. 1.
Example 2
The procedure is as in example 1, except that triphenylphosphine oxide is used in an amount of 4.23g (AlCl)3The mol ratio of the aluminum powder to the triphenylphosphine oxide is 1:7.5), and the obtained product nano aluminum powder is recorded as No. 2.
Example 3
The procedure is as in example 1, except that triphenylphosphine oxide is used in an amount of 5.63g (AlCl)3The molar ratio of the aluminum powder to the triphenylphosphine oxide is 1:10), and the obtained product nano aluminum powder is marked as No. 3.
Example 4
The procedure is as in example 1, except that triphenylphosphine oxide is used in an amount of 7.04g (AlCl)3The mol ratio of the aluminum powder to the triphenylphosphine oxide is 1:12.5), and the obtained product nano aluminum powder is marked as No. 4.
Example 5
The procedure is as in example 1, except that triphenylphosphine oxide is used in an amount of 8.45g (AlCl)3The molar ratio of the aluminum powder to the triphenylphosphine oxide is 1:15), and the obtained product nano aluminum powder is marked as No. 5.
Examples of the experiments
XRD spectrogram determination of nano aluminum powder prepared in Experimental example 1
Copper target and K α1And (3) determining the samples No. 1-5 under the condition of rays, sequentially marking the prepared nano aluminum powder samples, placing the samples on a glass sheet, compacting the samples, comparing a diffraction pattern of the samples with a standard aluminum powder pattern by XRD (X-ray diffraction), and scanning at 8 degrees/min. The results are shown in FIGS. 1.1 and 1.2.
An X-ray diffractometer (XRD), an abbreviation of X-ray diffraction, is a means for obtaining information such as the composition of a material, the structure or morphology of atoms or molecules inside the material, and the like by performing X-ray diffraction on the material and analyzing the diffraction pattern thereof. XRD was used to analyze the phase structure of the target sample. FIG. 1.1 shows that product spectra of different triphenylphosphine oxide dosages are combined together when the No. 1-5 nano aluminum powder samples are plotted by origin software, and FIG. 1.2 shows that XRD spectra of the No. 1 nano aluminum powder product in example 1 are combined with a standard spectrum (B) by JADE software, so that two nano aluminum powder pictures are obtained together, and the peak shape and the peak height spectrum of each picture are basically similar.
In FIG. 1.2, the upper layer (A) represents a spectrum of the product obtained in example 1; the lower layer (B) represents a standard map of aluminum powder.
The average particle size of the nano-aluminum is calculated by using the scherrer formula, and the result is detailed as shown in fig. 2:
D＝Kγ/βcosθ
(K is the Scherrer constant, D is the average thickness of the crystal grain vertical to the crystal plane direction, β is the half-height width of the diffraction peak of the measured sample, theta is the diffraction angle, gamma is the X-ray wavelength)
FIG. 1.1 is an XRD diffraction pattern of nano-aluminum powder prepared under different protective agents, and it can be seen that the intensity of the diffraction peak of the sample gradually weakens with the increase of the proportion of the protective agent, probably because the generated crystal nuclei are not grown up by the protective agent in time when the dosage of the protective agent is increased, and probably because the solvent effect of the solvent hinders the collision among the crystal nuclei, so that the surfaces of the sample participating in diffraction become less and less.
Fig. 1.2 is a graph comparing the XRD pattern of the product nano-aluminum powder sample of example 1 with the standard pattern.
Fig. 2 is a graph of the average particle size of the nano aluminum powder calculated by using the scherrer equation, and it can be known that the average particle size gradually decreases and tends to be stable, which is probably because the protective effect of the protective agent is not increased when the dosage of the protective agent reaches a certain amount.
In conclusion, with the increase of the dosage of the triphenylphosphine oxide (TPPO) protective agent, the surfaces of the nano aluminum participating in diffraction are less and less, and the defects of the sample are more and more; the particle size of the obtained product is gradually reduced and the protective effect of the protective agent tends to be stable.
Experimental example 2 Infrared Spectrometry of Nano-sized aluminum powder obtained
Carrying out infrared spectrum determination analysis on the sample No. 1-5, observing the absorption spectrum of the obtained nano aluminum powder, and judging whether the surface of the nano aluminum powder is coated by triphenylphosphine oxide (TPPO); the results are shown in FIG. 3.
The infrared absorption spectrum is generated by the continuous vibration and rotation of molecules, and the molecular vibration means that each atom in the molecules makes relative motion near an equilibrium position, and polyatomic molecules can form various vibration patterns. When each atom in a molecule performs simple vibration near an equilibrium position at the same frequency and the same phase, the vibration mode is called simple vibration (e.g., stretching vibration and variable angle vibration). The energy of molecular vibration corresponds exactly to the photon energy of infrared rays, so that when the vibrational state of the molecules changes, infrared spectra can be emitted, and infrared absorption spectra can also be generated by exciting the molecules to vibrate due to infrared radiation. Since each molecule has a unique infrared absorption spectrum determined by its composition and structure, when a beam of infrared rays of different wavelengths is irradiated onto a molecule of a substance, some of the infrared rays of a specific wavelength are absorbed to form an infrared absorption spectrum of the molecule, whereby the molecule can be subjected to structural analysis and identification.
In the figures, the numbers 1 to 5 represent anhydrous AlCl3The molar ratio of triphenylphosphine oxide (TPPO) to TPPO is 1: 5; 1: 7.5; 1: 10; 1: 12.5; the infrared spectrum at the ratio of 1:15, namely the infrared spectrum of the products of the examples 1-5, and TPPO is the infrared spectrum of the triphenylphosphine oxide monomer serving as a protective agent. From the figure, 2981cm-1The peak at (A) may be a stretching vibration mode of C-H stretching, which indicates that the sample contains anisole as a solvent; at 3070cm-1The peak at (A) is the vibrational peak of the C-H bond on the benzene ring, which is comparable to the actual 3080cm-1If the aluminum is not matched with the protective agent, the aluminum is probably red-shifted, which indicates that the nano aluminum is coordinated with the oxygen on the protective agent and the solvent; at 1610cm-1The peak is the stretching vibration of the C ═ C bond on the benzene ring, and the two indicate that the sample contains the benzene ring; at 1178cm-1And in742cm-1The peak at (C) is likely to be associated with the ring deformation vibration of the ring C-H wobble. 668cm-1The peak at position (A) is that Al coordinates with O to form an Al-O bond at 1397cm-1And 1129cm-1The peak at (a) may be the vibration of the P ═ O bond, indicating that the sample contained the protectant TPPO; the above results may indicate that the protective layer of the sample contains anisole and triphenylphosphine oxide; at 1581cm-1The resonance at (C) may be attributed to the stretching vibration of the C-C bond, 916cm-1，852cm-1And 692cm-1The peak at (A) may be the deformation vibration of the ring, which confirms that the mono-substituted benzene has an adsorption effect. The sattler manual for infrared spectroscopy is consulted to obtain: in this infrared spectrum, it is likely that the coordination bond between oxygen and aluminum ion causes movement of low wave number. The movement of the nanoparticles may be prevented or slowed down due to the Al atom forming a coordinate bond with the oxygen in triphenylphosphine oxide. And the triphenylphosphine oxide coated on the surface of the aluminum can play double roles of preventing the aggregation of the nano particles and protecting the nano particles from oxidation, and the triphenylphosphine oxide coated on the surface of the aluminum has larger molecules, so that the three-dimensional blocking effect can further prevent the aggregation of the nano particles, the particle size of the nano aluminum is small, and the stability of the nano aluminum is also improved.
Experimental example 3 thermogravimetric analysis of nano aluminum powder obtained
Thermogravimetric analysis was performed on the product No. 3 of example 3, with nitrogen as an atmosphere, at a temperature of 10 ℃ per minute and up to 800 ℃, and the thermal stability and the difference between the melting point and the normal melting point of the prepared nano-aluminum were observed. The results are shown in FIG. 4.
Thermogravimetric Analysis (TG-DSC) refers to a thermal Analysis technique for measuring the relationship between the mass of a sample to be measured and the temperature change at a programmed temperature, and is used to study the thermal stability and components of a material. It can be used to demonstrate the presence of triphenylphosphine oxide (TPPO), and fig. 4 is a thermogravimetric analysis of the nano-aluminum sample at room temperature to 800 ℃ in a nitrogen atmosphere. As shown in the figure, the melting point of the TPPO protective layer is 159 ℃, and the volatilization temperature is 291 ℃. From the DSC heat absorption peak, nearly 25% of the sample mass is lost and the triphenylphosphine oxide is completely burned out when 327 ℃ is reached, which indicates that nearly 60% of the sample mass is aluminum. Nano-aluminum begins to melt when the temperature reaches 622 ℃, which is nearly 40 ℃ lower than the melting point of most conventional aluminum materials. The experimental result reflects the characteristic of low melting point of the nano aluminum powder metal material provided by the invention.
The preparation method of the nano aluminum powder provided by the invention adopts anhydrous AlCl3And LiAlH4Reacting, namely preparing the nano aluminum powder by a solution chemical method and adding a protective agent triphenylphosphine oxide. The phase structure, the surface structure and the phase property of the sample are characterized by a series of experiments such as X-ray diffraction (XRD), infrared spectrum (IR), thermogravimetric analysis, particle size analysis and the like. When the ratio of the aluminum trichloride to the triphenylphosphine oxide is 1:5, 1:7.5, 1:10, 1:12.5 and 1:15, the nano aluminum particles are gradually reduced along with the increase of the ratio. Therefore, when the ratio is 1:10, namely the dosage of triphenylphosphine oxide is 5.63g, the nano aluminum particles are smallest, the morphology and the dispersion degree are best, and the effect of the nano aluminum powder prepared by the solution chemical method is best.
The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.
Claims (10)
1. A method for preparing nano aluminum powder is characterized by comprising the following steps:
step 1, weighing aluminum salt I and solvent I in a reaction vessel, and optionally mixing;
step 2, dispersing an aluminum salt II in a solvent II;
step 3, reacting the system in the step 2 with the system in the step 1;
and 4, carrying out post-treatment to obtain the nano aluminum powder.
2. The method according to claim 1, wherein, in step 1,
the aluminum salt I is an aluminum salt soluble in water or an organic solvent, preferably a single aluminum salt or a composite salt of aluminum and an alkali metal, and more preferably lithium aluminum hydride;
the solvent I is a polar organic solvent, preferably an ether solvent such as anisole, phenetole, diphenyl ether, more preferably anisole.
3. The method according to claim 1, wherein in step 1, the mixing means comprises stirring or ultrasonic oscillation, preferably ultrasonic oscillation, so that the mixing is uniform.
4. The method according to claim 1, wherein in step 1, a protecting agent is further added, wherein the protecting agent is an organic phosphine oxide compound and comprises alkyl phosphine oxide, aryl phosphine oxide and alkyl aryl phosphine oxide, preferably aryl phosphine oxide.
5. The method of claim 4, wherein the protecting agent is triphenylphosphine oxide.
6. The method according to claim 1, wherein in step 2, the aluminum salt II is an aluminum salt soluble in water or an organic solvent, preferably a single aluminum salt or a complex salt of aluminum and an alkali metal, more preferably aluminum trichloride; and/or
The solvent II is the same as the solvent I.
7. The method according to one of claims 1 to 6,
in the step 3, under the protection of inert gas, dropwise adding the aluminum salt II solution mixed in the step 2 into the mixed solution of the system in the step 1, controlling the reaction temperature and the dropwise adding time during dropwise adding, continuing to react until the reaction is complete, stopping heating, cooling to room temperature, and/or
The reaction temperature during dripping is 140-170 ℃.
8. The process according to claim 7, characterized in that the molar ratio of the aluminium salt II to the protective agent is 1: (2-25), preferably 1: (3-20).
9. The method according to claim 1, wherein in the step 4, the post-treatment comprises centrifuging the reaction solution, after the centrifugation is finished, washing and centrifuging the solid by using a solvent III, then washing by using a solvent IV, and then drying to obtain nano aluminum powder; and/or
The solvent III is absolute ethyl alcohol, and the solvent IV is acetone.
10. The nano-aluminum powder prepared by the method according to any one of claims 1 to 9, wherein the nano-aluminum powder has a small average particle size, preferably 20 to 60nm, and more preferably, the melting peak of the nano-aluminum powder is lower than the melting point of a conventional aluminum material, for example, about 40 ℃ lower, and particularly about 622 ℃.
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