Method for measuring content of aluminum in composite propellant

Abstract

The invention discloses a method for measuring the content of aluminum in a composite propellant, which comprises the following steps: digesting a sample by using nitric acid and hydrogen peroxide through microwaves, and then fixing the volume and diluting to prepare a sample solution; aluminum element standard solutions with a series of concentrations are prepared, the spectral intensity of the standard solutions is measured through inductively coupled plasma emission spectroscopy, and a standard curve is drawn; and measuring the sample solution under the same condition, calculating the aluminum element concentration through the standard curve, and further calculating the aluminum content in the sample. The method is simple to operate, low in reagent consumption, high in detection efficiency and good in repeatability, has no special requirements on the types of the components of the composite propellant, has universality and can be used for determining the aluminum content in the composite propellant.

Description

Technical Field

[0001] The invention belongs to the field of explosive analysis and testing, and relates to a method for determining the aluminum content in a composite propellant. Background Art

[0002] Metal aluminum has the characteristics of high density, high mass combustion heat and high volumetric combustion heat. It has a significant effect on improving the energy performance of explosives, and its raw materials are abundant, so it is widely used in explosives. Aluminum powder, as a high-energy combustion agent, is one of the important components of composite propellants. It releases a large amount of heat when burning, which can increase the combustion temperature of the propellant, thereby increasing the energy density and specific impulse. The content of each chemical component in the composite propellant is an important indicator for testing the quality of the product. Therefore, accurate determination of aluminum content is of great significance for the quality control of propellant products.

[0003] In the quantitative analysis of explosive components, there are two main methods for determining aluminum content. One is solvent extraction, also known as weight method, and the other is complexometric titration, also known as volumetric method. Solvent extraction method uses the difference in solubility of explosive components in different solvents or the ability to react with acids and alkalis, and washes the sample with different reagents in turn, so that each component is dissolved or eluted after reaction. The weight difference of the sample before and after washing is weighed to calculate the content of each component. This method has high accuracy and can obtain the content of multiple components in one test, but the test sample volume is large, the reagents consumed are large, the operation is cumbersome and time-consuming; in addition, this method is only suitable for explosive samples with relatively simple composition. For composite propellants, it contains multiple components such as binders, plasticizers, and curing agents. The polymer materials formed after chemical cross-linking are very easy to adhere to and cover other components, and it is difficult to be completely dissolved and washed by solvents. Therefore, this method cannot be used to determine the aluminum content. Complexometric titration is to digest the sample with an oxidizing strong acid, add excess EDTA to complex with aluminum ions, and then back-titrate with a zinc salt or lead salt standard solution to calculate the aluminum content. This method uses many types of reagents and has high requirements for operators. It mostly uses a nitric acid-perchloric acid system for wet digestion at normal pressure. The digestion reaction is violent and the perchloric acid used is highly dangerous. In addition, composite propellants generally contain inorganic salts such as lead and copper as combustion catalysts. These metal ions will interfere with titration. Therefore, this method is only suitable for the determination of aluminum content in explosive products that do not contain other metal components. Summary of the invention

[0004] In view of the shortcomings in the prior art, the purpose of the present invention is to provide a method for determining the aluminum content in a composite propellant, which uses microwave digestion for sample pretreatment and uses inductively coupled plasma emission spectroscopy to measure the aluminum content, thereby overcoming the problems of large sample volume, complex operation, time-consuming test, and high reagent consumption in traditional methods, and has no special requirements for the types of composite propellant components, and the method has universal applicability. The present invention can reduce the operational difficulty of sample preparation and testing, improve detection efficiency, and realize accurate and rapid determination of aluminum content in composite propellants.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0006] A method for determining the aluminum content in a composite propellant comprises the following steps:

[0007] Step 1, sample pretreatment: accurately weigh the composite propellant sample in a microwave digestion tank, add concentrated nitric acid, heat to make the aluminum powder fully react, cool to room temperature, add concentrated nitric acid and 30% hydrogen peroxide solution; use a microwave digestion instrument to digest; after digestion, heat to drive out the acid; dilute the sample to prepare a sample reserve solution, and then dilute the sample reserve solution according to the aluminum content range in the composite propellant to obtain a sample solution so that its concentration is within the concentration range of the prepared standard solution;

[0008] Step 2, standard solution preparation: prepare a series of aluminum standard solutions with concentrations ranging from 0 to 10 μg / mL;

[0009] Step 3, drawing a standard curve: using an inductively coupled plasma emission spectrometer to measure the spectral intensity of the aluminum element in the standard solution, and drawing a standard curve with the concentration of the aluminum element as the abscissa and the spectral intensity as the ordinate;

[0010] Step 4, sample determination: Use an inductively coupled plasma emission spectrometer to measure the spectral intensity of the sample solution under the same conditions as step 3, and then calculate the concentration of aluminum in the sample solution according to the standard curve drawn in step 3, and then calculate the aluminum content in the composite propellant sample.

[0011] The present invention also includes the following technical features:

[0012] Specifically, in step 1, the aluminum content of the composite propellant sample is in the range of 1% to 30%.

[0013] Specifically, in step 1, the addition ratio of the composite propellant sample, the concentrated nitric acid added for the first time, the additional concentrated nitric acid and the hydrogen peroxide solution is: 0.1 g to 0.2 g: 8 mL: 1 mL: 1 mL.

[0014] Specifically, the sample is weighed to an accuracy of 0.0001 g.

[0015] Specifically, in step 1, the conditions for heating the aluminum powder to fully react are: heating at 100° C. for 20 min to 30 min to fully react the aluminum powder.

[0016] Specifically, the microwave digestion conditions in step 1 are: programmed temperature, 150° C. for 10 min, 170° C. for 5 min, and 190° C. for 15 min.

[0017] Specifically, in step 1, after digestion is completed, heating to drive out the acid is performed at 140° C. to 150° C. until the sample residue is 1 mL to 2 mL.

[0018] Specifically, the dilution multiple of the sample stock solution in step 1 is 5 to 50 times.

[0019] Specifically, the standard solution preparation process of step 2 is: respectively transfer 0, 1.00, 2.00, 3.00, 5.00, and 10.00 mL of a 100 μg / mL aluminum standard solution into 6 100 mL volumetric flasks, respectively add 1 mL of concentrated nitric acid, and then dilute to 100 mL.

[0020] Specifically, the test conditions of the inductively coupled plasma emission spectrometer in step 3 and step 4 are: RF power 1150 W; auxiliary gas flow rate 0.5 L / min; nebulizing gas flow rate 0.5 L / min; cooling gas flow rate 12.5 L / min; nebulizer gas pressure 2.0 bar; peristaltic pump speed 45 rpm; injection time 30 s; integration time 15 s; repetition number 3 times; horizontal observation mode; aluminum element analysis line 396.152 nm.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (1) The microwave digestion sample pretreatment method provided by the present invention is simple, requires less reagents, and has high sample processing efficiency. The use of nitric acid-hydrogen peroxide as a digestion system can avoid the danger of using explosive perchloric acid.

[0023] (2) The present invention adopts inductively coupled plasma emission spectroscopy to determine the aluminum content in the composite propellant, which has simple operation, fast detection speed, high detection accuracy and good repeatability.

[0024] (3) Compared with the traditional solvent extraction method and complexometric titration method, the present invention has no special requirements on the types of sample components for testing the aluminum content of composite propellants, and the method has strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the standard curve of aluminum element. DETAILED DESCRIPTION

[0026] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0027] Embodiment 1:

[0028] This embodiment provides a method for determining the aluminum content in a composite propellant, wherein composite propellant A (theoretical aluminum content 16%±2%) is tested for aluminum content using the technical solution of the present invention, comprising the following steps:

[0029] Step 1, sample pretreatment: accurately weigh 0.1g-0.2g of composite propellant sample, accurate to 0.0001g, add 8mL of concentrated nitric acid in a microwave digestion tank, heat at 100°C for 20min-30min to make the aluminum powder fully react, add 1mL of concentrated nitric acid and 1mL of 30% hydrogen peroxide solution after cooling to room temperature; use a microwave digestion instrument to adopt a program heating, digest at 150°C for 10min, 170°C for 5min, and 190°C for 15min; after digestion, heat at 140°C-150°C to drive out the acid until the sample remains 1mL-2mL; dilute the sample to 100mL to prepare a stock solution, and dilute the sample stock solution 50 times according to the aluminum content in the composite propellant.

[0030] Step 2, preparation of standard solution: pipette 0, 1.00, 2.00, 3.00, 5.00, and 10.00 mL of 100 μg / mL aluminum standard solution into 6 100 mL volumetric flasks, add 1 mL of concentrated nitric acid to each flask, and then dilute to 100 mL.

[0031] Step 3, drawing a standard curve: using an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the spectral intensity of the aluminum element in the standard solution, and drawing a standard curve with the concentration of the aluminum element as the horizontal axis and the spectral intensity as the vertical axis.

[0032] The test conditions are as follows: RF power 1150W; auxiliary gas flow rate 0.5L / min; nebulizing gas flow rate 0.5L / min; cooling gas flow rate 12.5L / min; nebulizer gas pressure 2.0bar; peristaltic pump speed 45rpm; injection time 30s; integration time 15s; repetition number 3 times; horizontal observation mode; aluminum element analysis spectrum line 396.152nm.

[0033] Step 4, sample determination: Use ICP-OES to measure the spectral intensity of the sample solution under the same conditions as step 3, and then calculate the concentration of aluminum in the sample solution based on the standard curve drawn in step 3, and then calculate the aluminum content in the composite propellant sample.

[0034] Each sample was tested twice in parallel, and the test results are shown in Table 1.

[0035] Table 1 Test results of composite propellant samples

[0036]

[0037] The following is a further effect test of the method of Example 1:

[0038] (1) Linear range of the standard curve

[0039] The prepared aluminum standard solutions of 0 μg / mL (blank), 1 μg / mL, 2 μg / mL, 3 μg / mL, 5 μg / mL and 10 μg / mL were used to determine the aluminum content according to the technical scheme of the present invention. A standard curve was drawn with the concentration of aluminum as the abscissa and the spectral intensity as the ordinate. Figure 1 The linear correlation coefficient of the standard curve was 0.999.

[0040] (2) Detection limit of the method

[0041] The aluminum concentration of the blank solution was measured 12 times in parallel according to the method of Example 1, and the average value and standard deviation (SD) were calculated. The detection limit was calculated based on 3 times the standard deviation. The results are shown in Table 2.

[0042] Table 2 Detection limits of the methods

[0043]

[0044] (3) Repeatability of the method

[0045] Six samples of Example 1 were taken and measured according to the method of Example 1. The test results are shown in Table 3. The relative standard deviation RSD is less than 1%, indicating that the method of Example 1 has good repeatability and high precision.

[0046] Table 3 Repeatability test results of the method

[0047]

Claims

1. A method for determining the aluminum content in a composite propellant, characterized in that: The following steps are involved: Step 1, sample pretreatment: accurately weigh the composite propellant sample in a microwave digestion tank, add concentrated nitric acid, heat to make the aluminum powder fully react, cool to room temperature, add concentrated nitric acid and 30% hydrogen peroxide solution; use a microwave digestion instrument to digest; after digestion, heat to drive out the acid; dilute the sample to prepare a sample reserve solution, and then dilute the sample reserve solution according to the aluminum content range in the composite propellant to obtain a sample solution so that its concentration is within the concentration range of the prepared standard solution; Step 2, standard solution preparation: prepare a series of aluminum standard solutions with concentrations ranging from 0 to 10 μg / mL; Step 3, drawing a standard curve: using an inductively coupled plasma emission spectrometer to measure the spectral intensity of the aluminum element in the standard solution, and drawing a standard curve with the concentration of the aluminum element as the abscissa and the spectral intensity as the ordinate; Step 4, sample determination: Use an inductively coupled plasma emission spectrometer to measure the spectral intensity of the sample solution under the same conditions as step 3, and then calculate the concentration of aluminum in the sample solution according to the standard curve drawn in step 3, and then calculate the aluminum content in the composite propellant sample.

2. The method for determining the aluminum content in a composite propellant according to claim 1, characterized in that: In the step 1, the aluminum content of the composite propellant sample ranges from 1% to 30%.

3. The method for determining the aluminum content in the composite propellant according to claim 2, characterized in that: In the step 1, the addition ratio of the composite propellant sample, the concentrated nitric acid added for the first time, the additional concentrated nitric acid and the hydrogen peroxide solution is: 0.1 g to 0.2 g: 8 mL: 1 mL: 1 mL.

4. The method for determining the aluminum content in the composite propellant according to claim 3, characterized in that: Weigh the sample to an accuracy of 0.0001 g.

5. The method for determining the aluminum content in a composite propellant according to claim 1, characterized in that: In step 1, the conditions for heating the aluminum powder to fully react are: heating at 100° C. for 20 min to 30 min to fully react the aluminum powder.

6. The method for determining the aluminum content in a composite propellant according to claim 1, characterized in that: The microwave digestion conditions in step 1 are: programmed temperature, 150° C. for 10 min, 170° C. for 5 min, and 190° C. for 15 min.

7. The method for determining the aluminum content in a composite propellant according to claim 3, characterized in that: In the step 1, after the digestion is completed, heating to drive out the acid is performed at 140° C. to 150° C. until the sample remains in the range of 1 mL to 2 mL.

8. The method for determining the aluminum content in a composite propellant according to claim 3, characterized in that: The dilution multiple of the sample stock solution in step 1 is 5 to 50 times.

9. The method for determining the aluminum content in a composite propellant according to claim 1, characterized in that: The standard solution preparation process of step 2 is as follows: 0, 1.00, 2.00, 3.00, 5.00, and 10.00 mL of a 100 μg / mL aluminum standard solution are respectively transferred into 6 100 mL volumetric flasks, 1 mL of concentrated nitric acid is added to each flask, and then the volume is fixed to 100 mL.

10. The method for determining the aluminum content in a composite propellant according to claim 1, characterized in that: The test conditions of the inductively coupled plasma emission spectrometer in step 3 and step 4 are as follows: RF power 1150 W; auxiliary gas flow rate 0.5 L / min; nebulizing gas flow rate 0.5 L / min; cooling gas flow rate 12.5 L / min; nebulizer gas pressure 2.0 bar; peristaltic pump speed 45 rpm; injection time 30 s; integration time 15 s; repetition number 3 times; horizontal observation mode; aluminum element analysis line 396.152 nm.

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