A rapid characterization method for nanoparticle aluminum aluminum oxide film porosity

Abstract

The application provides a rapid characterization method for porosity of an aluminum oxide film of nano-aluminum particles, comprising the following steps: step one, taking a transmission electron microscope (TEM) photo by using a transmission electron microscope; the diameter d of a single particle and the diameter d2 of elemental aluminum nucleus are measured by a circular approximation method, and then the aluminum oxide layer thickness delta is obtained by subtracting the diameter d of the single particle from the diameter d2 of the elemental aluminum nucleus; step two, adjusting the mode of the transmission electron microscope to a scanning transmission mode, and performing energy spectrum scanning by using an in-situ energy dispersive X-ray spectrometer; the atomic number proportion w of oxygen elements in the whole particle is obtained by using a normalization method O ; step three, the nano-aluminum is composed of the elemental aluminum nucleus and the amorphous aluminum oxide shell layer, and the porosity P is calculated according to the parameters obtained in the steps one and two. The method can obtain the porosity of a single aluminum oxide layer in the nano scale, and can more truly reflect the coating strength of the aluminum oxide layer, and the method is simple, rapid and accurate.

Description

Technical Field

[0001] This invention belongs to the field of energetic materials technology, and relates to the detection of energetic materials, specifically to a rapid characterization method for the porosity of alumina films made of nano-aluminum particles. Background Technology

[0002] Nano-aluminum powder possesses high reactivity and reacts rapidly with oxidizers, releasing a large amount of heat. In the field of energetic materials, nano-aluminum powder is an excellent high-energy metallic combustion agent. Adding nano-aluminum powder to propellants can significantly improve their combustion rate, specific impulse, and density. Adding nano-aluminum powder to mixed explosives can greatly enhance their power. However, nano-aluminum powder has a high specific surface area and high reactivity, making it highly susceptible to oxidation in air and causing it to lose its excellent properties. Therefore, a small amount of oxygen is introduced during the preparation process, and passivation treatment is performed at a certain temperature to form an alumina film on its surface. The passivated alumina film is much thinner than the naturally oxidized alumina film and can inhibit further oxidation reactions between oxygen in the air and aluminum. The chemical composition of the alumina film is generally amorphous aluminum oxide (Al₂O₃), uniformly coating the surface of elemental aluminum cores. Studies have shown that during the combustion of nano-aluminum powder, the alumina film first ruptures, exposing the molten aluminum droplets inside to the external oxidizing environment, subsequently igniting. Therefore, the density of the alumina film coating is one of the important factors affecting the ignition efficiency of nano-aluminum powder. Porosity is an important parameter for quantitatively evaluating the density of the coating, so it is of great significance to rapidly and accurately characterize the porosity of the alumina film of nano-aluminum powder.

[0003] Currently, methods for characterizing material porosity are mainly divided into two categories: indirect methods and direct methods. Indirect methods include gravimetric methods, density methods, gas adsorption methods, and mercury porosimetry. These methods primarily calculate the porosity P by measuring the pore volume V1 and apparent volume V2 using the following formula:

[0004]

[0005] These methods can only measure the total volume of interconnected micropores within a porous medium, and cannot measure the volume of non-interconnected pores. The calculated porosity is the effective porosity, not the absolute porosity. Direct methods include microwave detection, industrial CT, and scanning electron microscopy.

[0006] The principle of microwave detection is to obtain porosity by studying the properties of a material in terms of microwave reflection, scattering and transmission. This method has the advantages of being fast and non-destructive, but it is not suitable for detecting pores smaller than millimeters.

[0007] Industrial CT method obtains information about the porosity of a material by detecting the path length and energy attenuation of X-rays inside the material. This method has the advantages of being fast, non-destructive, and accurate, but the equipment cost is high, and there are certain requirements for sample size, so it cannot be used for single-particle nano-aluminum powder.

[0008] Scanning electron microscopy (SEM) is a method that uses backscattered images to statistically calculate the porosity of a material surface. This method is simple and intuitive, but it is a destructive test and can only be calculated statistically from surface porosity, so it cannot obtain the original pore parameters inside the material.

[0009] Although the above methods have many advantages, they have the following two shortcomings in characterizing the porosity of alumina layers of nano-aluminum particles: First, except for scanning electron microscopy, the above methods are not applicable to nano-sized aluminum particles, nor can they perform micro-area analysis of alumina layers; they can only obtain the macroscopic porosity of agglomerates. Second, although scanning electron microscopy can perform nano-scale micro-area analysis, it can only obtain surface information and cannot obtain the overall internal information of the alumina film.

[0010] To address the shortcomings of existing methods, a new, more practical, and accurate detection method needs to be developed. Summary of the Invention

[0011] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a rapid characterization method for the porosity of alumina films made of nano-aluminum particles, thereby solving the technical problem that the characterization methods in the existing technology are difficult to balance practicality and accuracy.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0013] A rapid characterization method for the porosity of alumina films made of nano-aluminum particles, comprising the following steps:

[0014] Step 1, Morphological and Dimensional Characterization:

[0015] Transmission electron microscopy (TEM) was used to take TEM images; the diameter d of a single particle and the diameter d2 of the elemental aluminum core were measured by the circular approximation method, and the thickness δ of the alumina layer was obtained by subtracting the two.

[0016] Step 2, in-situ elemental quantitative characterization:

[0017] The transmission electron microscope was set to scanning transmission mode, and energy dispersive X-ray spectroscopy was performed using an in-situ energy-dispersive X-ray spectrometer. The atomic proportion w of oxygen in the entire particle was obtained by normalization. O .

[0018] Step 3, Porosity Calculation:

[0019] The aforementioned nano-aluminum particles are spherical, consisting of a single-element aluminum core and an amorphous aluminum oxide shell. The particle diameter d, oxide layer thickness δ, and the proportion of oxygen atoms in the entire particle are obtained through steps one and two. O Calculate the porosity P.

[0020] Compared with the prior art, the present invention has the following technical effects:

[0021] The characterization method of this invention measures the diameter, oxide layer thickness, and oxygen atom ratio of nano-aluminum powder particles using transmission electron microscopy and in-situ energy-dispersive X-ray spectroscopy, and then calculates the porosity of the alumina layer. This method allows for obtaining the porosity of a single alumina layer at the nanoscale, more accurately reflecting the coating strength of the alumina layer, and is simple, fast, and accurate. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a single nano-aluminum particle.

[0023] Figure 2 This is a transmission electron microscope image of nano-aluminum particles.

[0024] Figure 3 Scope of elemental analysis.

[0025] Figure 4 Elemental energy spectrum.

[0026] Figure 5 Calculation results of element content.

[0027] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, all materials and devices used in this invention are those known in the art.

[0029] This invention provides a rapid method for characterizing the porosity of an alumina layer from nano-aluminum particles. The method utilizes transmission electron microscopy (TEM) and in-situ energy-dispersive X-ray spectroscopy (EDS). By measuring the diameter of the nano-aluminum powder particles, the oxide layer thickness, and the proportion of oxygen atoms using TEM and EDS, the porosity of the alumina layer is calculated. This method can obtain the porosity of a single alumina layer at the nanoscale, more accurately reflecting the coating strength of the alumina layer. Furthermore, the method is simple, rapid, and accurate.

[0030] In the following embodiments, the instruments and samples are:

[0031] Transmission electron microscope (Thermo Fisher Talos F200i); ultrathin copper mesh; ethanol (analytical grade); nano-aluminum powder (Xi'an Modern Chemistry Research Institute).

[0032] The following examples illustrate the preparation of the samples:

[0033] (1) Sample dispersion:

[0034] Measure about 3 ml of ethanol into a test tube, add an appropriate amount of nano aluminum powder until the liquid is slightly turbid, and finally place it in an ultrasonic cleaner for ultrasonic dispersion for 15 minutes.

[0035] (2) Copper mesh sample preparation:

[0036] Place the copper mesh for the transmission electron microscope (TEM) on filter paper. After drawing up the dispersion using a pipette, add two drops of the dispersion onto the copper mesh. Then, place the copper mesh and filter paper together in an infrared oven and bake for 5 minutes. Clean the copper mesh in a plasma cleaner for 30 seconds, and finally place it in the TEM for measurement.

[0037] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0038] Example:

[0039] This embodiment provides a rapid characterization method for the porosity of alumina films made of nano-aluminum particles, which includes the following steps:

[0040] Step 1, Morphological and Dimensional Characterization:

[0041] After locating individual nano-aluminum powder particles using a transmission electron microscope (TEM) at 15,000x magnification, the magnification was increased to 300,000x. The β angle perpendicular to the sample rod axis was kept at 0, and the α angle parallel to the sample rod axis was adjusted to 15°. TEM images were then taken. The diameter d of the individual particle and the diameter d2 of the elemental aluminum core were measured using the circular approximation method. The alumina layer thickness δ was then obtained by subtracting the two.

[0042] In this embodiment, a schematic diagram of the structure of a single nano-aluminum particle is shown below. Figure 1 As shown.

[0043] In this specific embodiment, after locating a single nano-aluminum powder particle at 15,000x magnification, the magnification was adjusted to 300,000x. Maintaining the β angle perpendicular to the sample rod axis at 0° and adjusting the α angle parallel to the sample rod axis at 15°, a photograph was taken, as shown below. Figure 2 As shown. The diameter d of a single particle was measured to be 61.91 nm and the diameter d2 of the elemental aluminum core was measured to be 57.90 nm using the circular approximation method. The difference between the two was then used to obtain the aluminum oxide layer thickness δ as 4.01 nm.

[0044] Step 2, in-situ elemental quantitative characterization:

[0045] The transmission electron microscope was set to scanning transmission mode, and the magnification was adjusted to make the image of the nanoparticles as clear as possible. The optimal parameters for the in-situ energy-dispersive X-ray spectrometer were selected: a scanning range of 10 keV and a pulse flux of 30 Kcps. Energy spectroscopy was performed within a 30 nm diameter range centered on the aluminum nanoparticles. The atomic proportion w of oxygen in the entire particle was obtained by normalization. O .

[0046] In this embodiment, the transmission electron microscope is specifically set to scanning transmission mode, and the magnification is adjusted to make the image of the nanoparticles as clear as possible. The target area for analysis is selected within a 30nm diameter circle centered on the aluminum nanoparticles. Figure 3 As shown. Optimized parameters for the in-situ energy-dispersive X-ray spectrometer were selected: scan range of 10 keV and pulse flux of 30 kcps. The elemental energy distribution of the nano-aluminum particles was obtained through scanning, as shown below. Figure 4 As shown. The atomic proportion w of oxygen in the entire particle was obtained by normalization. O The value is 0.0377, and the calculation result is as follows: Figure 5 As shown.

[0047] Step 3, Porosity Calculation:

[0048] The aforementioned nano-aluminum particles are spherical, consisting of a single-element aluminum core and an amorphous aluminum oxide shell. The particle diameter d, oxide layer thickness δ, and the proportion of oxygen atoms in the entire particle are obtained through steps one and two. O Calculate the porosity P.

[0049] Specifically, in step three, the porosity calculation process is as follows:

[0050] Step 301: Calculate the volume V of the elemental aluminum core using Equations 2 and 3, based on the single particle diameter d and the oxide layer thickness δ. AL and the volume V of the oxide layer AL2O3 .

[0051]

[0052]

[0053] Step 302, combining the volume V of the elemental aluminum core AL Density ρ AL The relative molecular mass M of aluminum AL The amount of substance N in the elemental aluminum nucleus was calculated using Equation 4. AL .

[0054]

[0055] Step 302, by measuring the amount of oxygen N O The ratio of aluminum to elemental aluminum, combined with the ratio of oxygen atoms w O The mass m of the alumina layer is calculated using Equation 8. AL2O3 .

[0056]

[0057]

[0058]

[0059]

[0060] Step 303: Finally, calculate the apparent density of the alumina layer. Then, the porosity P is calculated using Equation 10.

[0061]

[0062]

[0063] In Equations 2 to 10:

[0064] d is the diameter of the nano-aluminum particles;

[0065] δ represents the thickness of the alumina layer;

[0066] V AL The volume of a single-element aluminum core;

[0067] The volume of the alumina layer;

[0068] N AL This represents the amount of elemental aluminum.

[0069] ρ AL The density of elemental aluminum is 2.7 g / cm³. 3 ;

[0070] M AL The relative molecular mass of aluminum is 26.98 g / mol;

[0071] w O This represents the proportion of oxygen atoms.

[0072] N O The amount of substance of oxygen atoms;

[0073] N' AL The amount of aluminum oxide;

[0074] N ALThis represents the amount of elemental aluminum.

[0075] The quality of the alumina layer;

[0076] The relative molecular mass of aluminum oxide is 101.96 g / mol;

[0077] The apparent density of aluminum oxide is calculated;

[0078] The actual density of aluminum oxide is 2.98 g / cm³. 3 .

[0079] In this embodiment, specifically, the diameter d of a single particle, the thickness δ of the alumina layer, and the atomic ratio w of oxygen are... O Substituting the values ​​into formulas 2, 3, 4, 5, 6, 7, 8, 9, and 10 in sequence, we obtain an alumina layer porosity P of 12.45%.

Claims

1. A rapid characterization method for the porosity of alumina films made from nano-aluminum particles, characterized in that, The method includes the following steps: Step 1, Morphological and Dimensional Characterization: Transmission electron microscopy (TEM) was used to capture TEM images; the diameter of the nano-aluminum particles was measured using the circular approximation method. d The diameter d2 of the elemental aluminum core is then subtracted from the diameter d2 to obtain the thickness δ of the alumina layer. Step 2, in-situ elemental quantitative characterization: The transmission electron microscope was set to scanning transmission mode, and energy dispersive X-ray spectroscopy was performed using an in-situ energy-dispersive X-ray spectrometer. The atomic proportion of oxygen in the entire particle was obtained by normalization. w O ; Step 3, Porosity Calculation: The aforementioned nano-aluminum particles are spherical, composed of a single aluminum core and an amorphous alumina shell. The diameter of the nano-aluminum particles obtained through steps one and two is... d The thickness δ of the alumina layer and the atomic proportion of oxygen in the entire particle. w O Calculate porosity P ; In step three, the specific process for calculating porosity is as follows: Step 301, by the diameter of the nano-aluminum particles d The volume of the elemental aluminum core was calculated using Equations 2 and 3, based on the thickness δ of the alumina layer. and the volume of the alumina layer ; Formula 2; Formula 3; Step 302, combining the volume of the elemental aluminum core Density of elemental aluminum and the relative molecular mass of aluminum The amount of elemental aluminum can be calculated using Equation 4. ; Equation 4; Step 303, by determining the amount of oxygen. The ratio of aluminum to elemental aluminum, combined with the atomic ratio of oxygen. w O The mass of the alumina layer was calculated using Equation 8. ; Formula 5; Formula 6; Formula 7; Formula 8; Step 304: Finally, calculate the apparent density of the alumina layer. Then, the porosity is calculated using Equation 10. P ; Equation 9; Formula 10; In Equations 2 to 10: The diameter of the nano-aluminum particles; The thickness of the alumina layer; The volume of the elemental aluminum core; The volume of the alumina layer; This represents the amount of elemental aluminum. The density of elemental aluminum is 2.7 g / cm³. 3 ; The relative molecular mass of aluminum is 26.98 g / mol; This represents the proportion of oxygen atoms. This refers to the amount of substance of oxygen. The quality of the alumina layer; The relative molecular mass of aluminum oxide is 101.96 g / mol; The apparent density of the alumina layer; The actual density of the alumina layer is 2.98 g / cm³. 3 .

2. The rapid characterization method for the porosity of alumina films made from nano-aluminum particles as described in claim 1, characterized in that, The specific process of step one is as follows: After locating individual nano-aluminum powder particles using a transmission electron microscope (TEM) at 15,000x magnification, the magnification is adjusted to 300,000x, keeping the β angle perpendicular to the sample rod axis at 0° and the α angle parallel to the sample rod axis at 15°, and a TEM image is taken; the diameter of the nano-aluminum particles is measured using the circular approximation method. d The diameter d2 of the elemental aluminum core is then subtracted from the diameter d2 to obtain the thickness δ of the alumina layer.

3. The rapid characterization method for the porosity of alumina films made from nano-aluminum particles as described in claim 1, characterized in that, Step two involves the following steps: The transmission electron microscope (TEM) is switched to scanning transmission mode, and the magnification is adjusted to ensure a clear image of the nanoparticles. The optimal parameters for the in-situ energy-dispersive X-ray spectrometer are selected: a scanning range of 10 keV and a pulse flux of 30 Kcps. An energy spectrum scan is performed within a 30 nm diameter range centered on the aluminum nanoparticles. The atomic proportion of oxygen in the entire particle is obtained using a normalization method. w O .

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