Method and system for testing equivalent water content in nitro oxidant

Abstract

The invention discloses a method and system for testing equivalent water content in a nitro oxidant, and the method comprises the following steps: (1) collecting near infrared spectrums of a plurality of nitro oxidant standard samples to form a near infrared spectrum set of the standard samples; (2) constructing a quantitative detection model of equivalent water content through a multivariate correction algorithm based on the near infrared spectrum set and the equivalent water content value of the nitro oxidant standard sample; (3) collecting the near infrared spectrum of a to-be-detected sample, and determining the equivalent water content by using the quantitative detection model; the nitro oxidant is selected from at least one of nitrogen tetroxide, nitrogen tetroxide containing nitric oxide and modified products thereof. The system comprises a near-infrared spectrometer, a temperature control device and a calculation processing unit. The test method provided by the invention has the advantages of stronger adaptability, wider applicability and higher test precision, and can realize rapid and accurate quantification of equivalent water content of various nitro oxidants under various environmental conditions and different sample pretreatment modes.

Description

Technical Field

[0001] This invention relates to the field of chemical testing, specifically to a method and system for testing the equivalent water content in nitro oxidants. Background Technology

[0002] Nitrogen tetroxide (N₂O₄) and green nitrogen tetroxide (MON) are widely used bicomponent nitro oxidants in liquid rocket engines. Besides free water, some of the water in both N₂O₄ and MON reacts with N₂O₄ to form nitric acid, and the two together constitute the equivalent water content. This equivalent water content has a critical impact on the quality of N₂O₄ and MON, directly affecting the propellant's corrosiveness to contact materials, thus influencing the propellant's storage stability and application reliability, and in severe cases, even affecting the success of space launches. The current national military standard GJB 1673A-2021, "Nitrogen Tetroxide Specification," includes near-infrared spectroscopy and gas chromatography for testing equivalent water content; GJB 1964A-2015, "Green Nitrogen Tetroxide Specification," includes near-infrared spectroscopy, gas chromatography, and microwave spectroscopy for testing equivalent water content. Both standards use near-infrared spectroscopy as the arbitration method.

[0003] The current national military standard's near-infrared detection method is based on single-wavelength detection. This involves selecting the absorbance at a specific wavelength and directly calculating the equivalent water content in nitrogen tetroxide based on the specific relationship between absorbance and water content. The key advantage of this method is its high detection speed, but it is relatively complex to operate. Whether it's nitrogen tetroxide or green nitrogen tetroxide, the sample must be oxidized before testing to completely oxidize the free water in the sample into nitric acid. Nitric acid has a specific absorption peak in the near-infrared region, and the equivalent water content is determined based on the magnitude of this absorption peak. Furthermore, this method suffers from significant instrument error and poor environmental adaptability. Even minor changes in the testing environment and the sample can affect the accuracy of the spectrum, and the single-wavelength method struggles to effectively correct for these variations, leading to unstable measurement results.

[0004] Multivariate molecular spectroscopy correction is a rapidly developing analytical technique that enables the simultaneous determination of multiple components without separation or masking. It involves using molecular spectra containing information about sample functional groups, composition, or physical states as a training set, and correlating them with compositional or property data obtained from standard or recognized reference methods to establish a multivariate correction model. For unknown samples, once their spectra are obtained, concentration or property parameters can be predicted based on the established model.

[0005] The problem that needs to be solved is how to use molecular spectroscopy multivariate correction technology to detect the equivalent water content in nitro oxidants and to accurately determine the equivalent water content of the test samples under various environmental conditions and different sample pretreatment methods.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome at least one of the shortcomings of the prior art and provide a method and system for testing the equivalent water content in nitro oxidants. This invention establishes a more adaptable and widely applicable method for testing the equivalent water content of nitro oxidants using molecular spectral multivariate correction technology. It can accurately determine the equivalent water content of samples under various environmental conditions and different sample pretreatment methods, and can serve as a supplementary method to the methods specified in the national military standard. To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for testing the equivalent water content in a nitro oxidant, comprising the following steps: (1) Collect near-infrared spectra of multiple nitro oxidant standard samples to form a near-infrared spectrum set of standard samples; (2) Based on the near-infrared spectral set and the equivalent water content values ​​of the nitro oxidant standard sample, a quantitative detection model for equivalent water content is constructed by a multivariate correction algorithm; (3) Collect the near-infrared spectrum of the sample to be tested, and use the quantitative detection model to determine the equivalent water content; The nitro oxidant is selected from at least one of dinitrogen tetroxide, dinitrogen tetroxide containing nitric oxide (green dinitrogen tetroxide MON), and their modified products.

[0008] Compared to the existing method of determining the equivalent water content in the form of nitric acid after complete oxidation by using a standard curve under single-wavelength measurement conditions, this invention utilizes multi-wavelength or wavelength range absorbance and establishes an equivalent water content model through a multivariate correction method. This can reduce random errors caused by absorbance signal fluctuations, be compatible with different sample pretreatment methods, better adapt to sample temperature fluctuations, and achieve higher detection efficiency and accuracy.

[0009] In a further step, in step (1), the standard sample is first subjected to spectral acquisition. Within a certain wavelength range in the near-infrared spectral region, the near-infrared spectrum of the nitro oxidant standard sample with an accurate equivalent water content value is acquired, forming a near-infrared spectral set of the standard sample. The acquired standard sample can be an equivalent water content standard substance or a precisely prepared sample. For the standard sample, the equivalent water content value is the equivalent water content determined by its preparation value or by other traceable methods.

[0010] Compared to existing single-wavelength measurement methods that can only measure the equivalent water content in the form of nitric acid after standardization, the near-infrared spectral multivariate correction method of this invention can analyze both the equivalent water content after standardization and the equivalent water content in different forms.

[0011] In a further step, in steps (1) and (3), the near-infrared spectrum is acquired using one of the following methods: a) Directly collect the near-infrared spectra of standard samples or samples to be tested; b) First, oxidize the water in the standard sample or the sample to be tested to convert it all into nitric acid, and then collect the near-infrared spectrum.

[0012] In a further embodiment, method b), oxygen is used to oxidize the equivalent water in the standard sample or the sample to be tested.

[0013] Furthermore, the oxidation treatment method includes: taking a sample into a glass oxidation bottle, introducing oxygen into the bottle, observing the change in oxygen flow rate, and shaking thoroughly until the flow rate is 0 to complete the oxidation of the sample.

[0014] As a preferred embodiment, the present invention acquires near-infrared spectra using method a).

[0015] The testing method of this invention is compatible with both oxidized and unoxidized samples. Before collecting the near-infrared spectra of the standard sample and the sample to be tested, the equivalent water in the sample can be oxidized with oxygen to convert it entirely into nitric acid, and then the near-infrared spectrum of the sample can be collected. The equivalent water content can be determined by analyzing the absorption spectrum information of nitric acid in the sample after oxidation treatment. Alternatively, the equivalent water in the sample can be directly collected without oxidation treatment, and the total equivalent water content can be predicted in one step by simultaneously analyzing multiple absorption peaks of various forms of water. In this way, for conventional samples, the cumbersome oxidation step can be eliminated, and direct measurement can be performed, greatly simplifying the operation process and improving the detection efficiency.

[0016] Furthermore, temperature alters the spectral characteristics of the analyte, such as the position and intensity of absorption peaks. Current single-wavelength methods for determining equivalent water content require strict control of spectral acquisition of all standard and analyte samples at the same temperature to eliminate errors caused by temperature variations. This places high demands on sample temperature control and instrument hardware. In multivariate calibration methods, the effect of temperature variation on the spectrum can be mitigated by acquiring spectra under multiple temperature conditions. By incorporating the temperature effect into the model, the spectral changes caused by temperature can be separated, enabling accurate determination of equivalent water content at a single measurement temperature or within a certain range of variation.

[0017] In a further proposed approach, during steps (1) and (3), the temperature control in the near-infrared spectral acquisition process shall employ one of the following methods: a) All standard samples and test samples were spectrally acquired at the same temperature; b) Within the set temperature range, select multiple different temperature conditions to collect spectra of the standard samples, and select one or more temperature conditions to collect spectra of each standard sample; the sample to be tested is collected at any temperature within the set temperature range.

[0018] This invention allows for spectral acquisition of all standard samples at the same temperature, and then of the test sample at that same temperature, ensuring the accuracy of the prediction results. Alternatively, it allows for spectral acquisition of standard samples under multiple different temperature conditions within a certain temperature range. Each standard sample can select one or more temperature conditions for spectral acquisition, making the model more temperature-adaptable, reducing the need for temperature control capabilities of the near-infrared spectrometer, minimizing the influence of ambient temperature on the test results, and improving the accuracy of the test results. When testing the test sample, spectral acquisition can be performed at any temperature within this temperature range. Specifically: The samples in Method a are all acquired at the same constant temperature, which can eliminate the spectral differences introduced by temperature variables to the greatest extent, providing a highly consistent thermodynamic environment for model building and prediction, and ensuring the accuracy and reproducibility of the model under ideal conditions.

[0019] Method b incorporates temperature variations into the model training beforehand, enabling the established quantitative analysis model to inherently possess the ability to compensate for and correct for the effects of temperature. This significantly enhances the model's adaptability, reduces the stringent requirements for constant temperature conditions during prediction, and allows it to maintain stable and reliable prediction results in real-world environments. This makes the analysis method adaptable to a wider range of field application scenarios.

[0020] As a preferred embodiment, during the near-infrared spectral acquisition process of the sample in this invention, temperature control adopts method b).

[0021] The boiling point of dinitrogen tetroxide is 21℃, the freezing point is -11℃, and the boiling point of green dinitrogen tetroxide is 18℃. The freezing point is in the range of -14℃ to -12℃. In order to maintain the physical state of the sample, in steps (1) and (3), when collecting near-infrared spectra, the temperature of the standard sample and the sample to be tested is controlled at -5℃ to 15℃.

[0022] A further approach involves using dry gas to continuously or intermittently purge the sample chamber of the spectrometer before, during, and after spectral acquisition, as the sample temperature is relatively low, to prevent condensation on the cuvette surface and ensure the accuracy of the test results.

[0023] A further approach involves acquiring near-infrared spectra using absorbance data mode, covering a spectral range of 1250 nm to 1950 nm.

[0024] Near-infrared spectra of nitro oxidant standard samples with accurate equivalent water content values ​​were collected within a specific wavelength range. Equivalent water in dinitrogen tetroxide and green dinitrogen tetroxide mainly exists in the form of free water and nitric acid. The absorption peaks of water in the near-infrared region are mainly at 1450 nm, 1940 nm, and 2200 nm, with strong absorption peaks at 1450 nm and 1940 nm. The absorption peaks of nitric acid are mainly at 1250 nm, 1470 nm, and 1750 nm, corresponding to different molecular vibrational frequencies and combination frequencies, respectively. When collecting spectra, absorbance data mode was used, referencing the absorption peak positions and intensities of water and nitric acid, as well as the spectral range that the near-infrared spectrometer can scan, covering the spectral range of 1250 nm to 1950 nm.

[0025] In a further step, in step (2), when establishing the quantitative analysis model, the spectral data used is selected from one of the following methods: a) Use absorbance data across all wavelengths collected; b) Select absorbance data within one or more wavelength ranges; c) Select absorbance data at multiple discrete characteristic wavelength points.

[0026] Method a uses all wavelength data, maximizing the utilization of all information in the spectrum and avoiding the omission of certain weak but crucial characteristic peaks due to subjective selection. Method b selects one or several characteristic wavelength ranges. By eliminating irrelevant or noisy bands, it can reduce the interference of extraneous variables, allowing the model to focus more on the spectral information most relevant to the target component; it can also speed up computation; the selected wavelength range corresponds to the combination and overtone absorption regions of specific molecular vibrations of the analyte (such as the NH bond of ammonium nitrate, the OH bond of water, and the CH bond of auxiliaries), which can enhance the model's interpretability. Method c selects multiple discrete characteristic wavelength points, resulting in the simplest model, strong resistance to overfitting, and high computational efficiency.

[0027] In a further step, in step (2), the near-infrared spectral set is first preprocessed, and then the preprocessed near-infrared spectral data containing absorbance at multiple wavelengths is correlated with the corresponding water content value through a multivariate correction algorithm to construct a quantitative detection model.

[0028] Multivariate correction techniques in molecular spectroscopy significantly improve the accuracy and stability of analysis in complex systems by canceling interference and optimizing signals using multi-wavelength information. Compared to single-wavelength testing, it changes from "single-point dependence" to "range verification." By selecting the target peak and non-interfering background region, the multivariate correction method can separate the target signal from the interference signal through algorithms, while taking into account multiple absorption peaks of the target component.

[0029] During sample acquisition, the sample's state, color, and instrument response often introduce interference from factors unrelated to the sample's properties into the raw near-infrared spectrum, leading to baseline drift and spectral instability. Therefore, preprocessing is essential. Since nitro oxidants are homogeneous red or green liquids, this invention compares one or more commonly used liquid preprocessing methods selected from baseline correction, standardization, mean centering, first derivative, second derivative, multivariate scattering correction, standard normal variable transformation, detrending, and Savitsky-Golay smoothing.

[0030] For example, preprocessing mainly includes one or more combinations of the following: eliminating baseline drift and tilt (which can be done by baseline correction and detrending), reducing noise interference (which can be done by Savitzky-Golay smoothing), enhancing spectral feature differences (which can be done by first derivative and second derivative), correcting scattering effects (which can be done by multivariate scattering correction and standard normal variable transformation), and standardizing data scales (which can be done by standardization and mean centering).

[0031] In a further embodiment, the multivariate correction algorithm is selected from one or more of the following: multivariate linear regression, principal component regression, and partial least squares.

[0032] When establishing the spectral model, the multivariate correction method is used. When modeling with absorbance data at a small number of discrete wavelengths, multivariate linear regression is used. When modeling with wavelength ranges containing a large number of wavelengths, principal component regression or partial least squares is used.

[0033] Secondly, the present invention provides a near-infrared spectroscopy analysis system for implementing the aforementioned test method, the system comprising: Near-infrared spectrometer, used to collect near-infrared spectra of standard samples and samples to be tested; Temperature control device, used to adjust and stabilize the temperature of the sample during spectral acquisition; The computing processing unit is configured as follows: Store the standard spectral dataset and the known content of each component; A multivariate correction algorithm is executed to establish the quantitative detection model; The spectrum of the sample to be tested is received, and the equivalent water content is calculated and output using the quantitative detection model.

[0034] Thirdly, the present invention provides a non-transitory computer-readable storage medium storing a computer program configured, when executed by a processor, to implement a method for testing the equivalent water content in the nitro oxidant.

[0035] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0036] (1) This invention establishes a method for testing the equivalent water content of nitro oxidants based on molecular spectral multivariate correction technology. Compared with the existing standard method based on the near-infrared method of single-wavelength detection, this method has the advantages of stronger adaptability and wider applicability. The multivariate correction technology can simultaneously process the overlapping signals of multiple components. By modeling the multi-wavelength signals, it can cancel background interference and the interaction between components, and significantly reduce the measurement uncertainty caused by the random fluctuation of absorbance of a single wavelength, thereby reducing the error and greatly improving the accuracy and stability of the test results.

[0037] (2) Current standard testing methods require the sample to be oxidized first, so that all the water content is uniformly converted into nitric acid before measurement. However, the test method developed in this invention can adapt to two different sample pretreatment methods: either the sample is fully oxidized before measurement as in the current standard method, or no oxidation treatment is required. By using multi-wavelength signal modeling, the total content of various forms of water in the sample can be directly determined. For routine samples, the cumbersome oxidation step can be omitted, and the measurement can be performed directly, thus simplifying the sample pretreatment process and improving detection efficiency.

[0038] (3) Current standard testing methods require that samples must be measured at a strictly fixed temperature. However, the testing method developed in this invention can adapt to the testing needs of samples under non-fixed temperature conditions. During spectral acquisition, variable temperature scanning is used to incorporate the spectra of samples at different temperatures within the range of -5℃ to 15℃ into the model, making the model more temperature adaptable (with temperature compensation capability), reducing the need for temperature control capability of the near-infrared spectrometer, ensuring the accuracy of test results under temperature variation conditions, and enhancing the practicality and environmental adaptability of the method.

[0039] (4) This invention explicitly includes green dinitrogen tetroxide (MON) and its modified products in the detection scope. By constructing a model containing multiple matrix standard samples, one model can be applied to multiple different types of nitro oxidants, realizing the universality of the method and avoiding the trouble of establishing independent analytical methods for each material, thus having a wider range of material adaptability.

[0040] Furthermore, current single-wavelength methods can only measure the total equivalent water that exists in the form of nitric acid after oxidation. However, this invention utilizes multi-wavelength information to directly and comprehensively analyze multiple absorption peaks of free water and nitric acid in the sample, thereby achieving a one-step, non-destructive measurement of the total content (equivalent water) of different forms of water and providing more comprehensive sample information.

[0041] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0042] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is the near-infrared spectrum of a standard sample of nitro oxidant; Figure 2 It is the fitting curve between the model prediction and the actual value of the equivalent water content.

[0043] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0045] Comparative Example 1 The steps for establishing the comparative standard curve in this invention are as follows: (1) Spectral acquisition: The absorbance at 1470 nm was measured. The absorbance was measured using standard substances (GBW13502~13509) with equivalent water content in dinitrogen tetroxide as standard samples (all of which were oxidized samples) and the temperature was controlled at 15℃. Nitrogen gas was introduced into the test chamber during the measurement to ensure that no fog was generated on the surface of the quartz colorimetric cell; (2) Plotting the standard curve: Plot the standard curve based on the absorbance at 1470 nm and the equivalent water content of the standard sample.

[0046] Example 1 The specific modeling steps for Model A in this embodiment are as follows: (1) Spectral acquisition: Instrument: Grating-type near-infrared spectrometer; Standard samples: Standard reference material for equivalent water content in dinitrogen tetroxide (GBW13502~13509); Parameters: Wavelength range of 1250 nm to 1950 nm; Operation and conditions: Scan all standard samples, one scan per standard sample, maintain sample temperature at 15℃, and collect near-infrared absorption spectra. During measurement, introduce nitrogen gas into the test chamber to ensure no fogging occurs on the surface of the quartz cuvette.

[0047] Near-infrared spectra of nitro oxidant standard samples are as follows: Figure 1 As shown.

[0048] (2) Establishment of quantitative model: Preprocessing: The raw near-infrared spectrum is subjected to "mean centering", "first derivative" and "de-trending" to eliminate baseline drift and enhance spectral features.

[0049] Band selection: The modeled spectral range is 1250 nm to 1950 nm.

[0050] Modeling algorithm: The collected near-infrared spectral data are fitted with the water content of the standard sample and processed to establish a quantitative detection model using partial least squares method.

[0051] Example 2 The specific modeling steps for Model B in this embodiment are as follows: (1) Spectral acquisition: Instrument: Grating-type near-infrared spectrometer; Standard samples: Standard reference material for equivalent water content in dinitrogen tetroxide (GBW13502~13509); Parameters: Wavelength range of 1250 nm to 1950 nm; Operation and conditions: Scan all standard samples, and collect near-infrared spectra for each standard sample at controlled temperatures of -5℃ and 15℃. During the measurement, nitrogen gas is introduced into the test chamber to ensure that no fog is generated on the surface of the quartz cuvette.

[0052] (2) Establishment of quantitative model: Preprocessing: The raw near-infrared spectrum is subjected to "mean centering", "first derivative" and "de-trending" to eliminate baseline drift and enhance spectral features.

[0053] Band selection: The modeled spectral range is 1250 nm to 1950 nm.

[0054] Modeling algorithm: The collected near-infrared spectral data are fitted with the equivalent water content of the standard sample through spectral processing. That is, the spectral data of each sample at two temperatures are correlated with the equivalent water content value, and a model is established using partial least squares method.

[0055] The fitting curves of the model predictions and actual values ​​for equivalent water content were analyzed using Model B, as shown below. Figure 2 As shown.

[0056] Example 3 The specific modeling steps for model C in this embodiment are as follows: (1) Spectral acquisition: Instrument: Grating-type near-infrared spectrometer; Standard samples: Multiple samples of dinitrogen tetroxide, MON-1 and MON-3 type green dinitrogen tetroxide products with water content ranging from 0.01% to 0.20% and whose water content has been accurately determined in advance are used as standard samples. No oxidation treatment is performed on the samples.

[0057] Parameters: Wavelength range of 1250 nm to 1950 nm; Operation and conditions: Scan all standard samples, one scan per standard sample, maintain sample temperature at 15℃, and collect near-infrared absorption spectra. During measurement, introduce nitrogen gas into the test chamber to ensure no fogging occurs on the surface of the quartz cuvette. (2) Establishment of quantitative model: Preprocessing: The raw near-infrared spectrum is subjected to "mean centering", "first derivative" and "de-trending" to eliminate baseline drift and enhance spectral features.

[0058] Band selection: The modeled spectral range is 1250 nm to 1950 nm.

[0059] Modeling algorithm: The collected near-infrared spectral data are fitted with the water content of the standard sample and processed to establish a quantitative detection model using partial least squares method.

[0060] Example 4 Two nitrogen tetroxide equivalent water content standard substances (GBW13502 and GBW13504) were used. The absorbance at 1470 nm and near-infrared spectra covering the wavelength range of 1250 nm to 1950 nm were measured at 15℃. Each sample was measured six times. The equivalent water content was analyzed using a comparative standard curve (Comparative Example 1), Model A (Example 1), Model B (Example 2), and Model C (Example 3), respectively. The results are shown in the table below: Table 1 Results analysis: It is evident that the equivalent water content results obtained by the four methods have good accuracy. Compared to the results measured using the single-wavelength standard curve method in Comparative Example 1, the standard deviation of the prediction results from the models constructed in Examples 1-3 of this invention is significantly reduced. This indicates that the equivalent water content results measured using the multivariate correction method of this invention have better method parallelism.

[0061] Example 5 Two nitrogen tetroxide equivalent water content standard substances (GBW13502 and GBW13504) were used. The absorbance at 1470 nm and near-infrared spectra covering the wavelength range of 1250 nm to 1950 nm were measured at 0℃, 10℃, and 15℃, respectively. The equivalent water content was analyzed using a comparative standard curve (Comparative Example 1), Model A (Example 1), and Model B (Example 2), respectively. The results are shown in the table below: Table 2 Results analysis: As can be seen from the results in Table 2, compared to the results of collecting data and establishing a standard curve and calibration model only at 15℃, Model B, which collected data and established a calibration model under multiple temperature conditions, showed more accurate prediction results at the different temperatures tested. Specifically: At 0℃, the calculated results of the comparison standard curve (Comparative Example 1) were significantly lower than the actual values, with a large error. Only as the temperature increased to the calibration temperature of 15℃ did the results gradually approach the true values. This demonstrates that the single-wavelength method is extremely sensitive to temperature, requiring very strict temperature control; otherwise, the results are unreliable.

[0062] Model A (Example 1) was established only at 15°C. When the test temperature deviated from 15°C, its prediction results were better than those of the traditional method, but still showed deviations (the predicted values ​​were lower at 0°C and 10°C).

[0063] Regardless of whether the tests were conducted at 0°C, 10°C, or 15°C, Model B (Example 2) consistently produced predictions for the two standard materials (GBW13502 and GBW13504) that were very close to their nominal values. This indicates that by incorporating spectral data from -5°C and 15°C into its training, Model B successfully "learned" to recognize and counteract the effects of temperature changes on the spectrum, thus maintaining high accuracy across different temperatures.

[0064] Example 6 One sample each of dinitrogen tetroxide and green dinitrogen tetroxide was taken. Without oxidation treatment, the absorbance at 1470 nm was measured at 15℃ and near-infrared spectra covering the wavelength range of 1250 nm to 1950 nm were collected. The equivalent water content was analyzed by comparison standard curve, model A and model C, respectively.

[0065] Among them, the production batch number of dinitrogen tetroxide is YI-202503, which was produced by the Beijing Aerospace Test Technology Research Institute; The green dinitrogen tetroxide production batch number is YIII-202406, and it was produced by the Beijing Aerospace Test Technology Research Institute.

[0066] The results are shown in the table below: Table 3 sample Compare the calibration curve calculation results (%) Model A prediction results (%) Model C prediction results (%) Unoxidized dinitrogen tetroxide 0.0199 0.0196 0.0215 Unoxidized green dinitrogen tetroxide 0.0415 0.0405 0.0463 In addition, using the near-infrared method, the standard method for determining equivalent water content in the national military standard GJB1673A-2021, the equivalent water content in the nitrogen tetroxide sample was measured to be 0.0209%. Using the near-infrared method, a standard method for determining equivalent water content in the national military standard GJB1964A-2015, the equivalent water content in the green nitrogen tetroxide sample was determined to be 0.0468%.

[0067] Results analysis: As shown in Table 3, the near-infrared spectral model C, established using unoxidized standard samples, yields relatively accurate results for unoxidized test samples. In contrast, the current standard method (comparison calibration curve) and the calibration model (model B) established using only oxidized samples exhibit significant errors in the equivalent water content test results for unoxidized samples.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for testing the equivalent water content in a nitro oxidant, characterized in that, Includes the following steps: (1) Collect near-infrared spectra of multiple nitro oxidant standard samples to form a near-infrared spectrum set of standard samples; (2) Based on the near-infrared spectral set and the equivalent water content values ​​of the nitro oxidant standard sample, a quantitative detection model for equivalent water content is constructed by a multivariate correction algorithm; (3) Collect the near-infrared spectrum of the sample to be tested, and use the quantitative detection model to determine the equivalent water content; The nitro oxidant is selected from at least one of dinitrogen tetroxide, dinitrogen tetroxide containing nitric oxide, and their modified products.

2. The test method according to claim 1, characterized in that, In steps (1) and (3), the near-infrared spectrum is acquired using one of the following methods: a) Directly collect the near-infrared spectra of standard samples or samples to be tested; b) First, oxidize the water in the standard sample or the sample to be tested to convert it all into nitric acid, and then collect the near-infrared spectrum.

3. The test method according to claim 1 or 2, characterized in that, In steps (1) and (3), during the near-infrared spectral acquisition process, temperature control is performed using one of the following methods: a) All standard samples and test samples were spectrally acquired at the same temperature; b) Within the set temperature range, select multiple different temperature conditions to collect spectra of the standard samples, and select one or more temperature conditions to collect spectra for each standard sample; The sample to be tested is subjected to spectral acquisition at any temperature within the set temperature range.

4. The test method according to claim 3, characterized in that, In steps (1) and (3), when collecting near-infrared spectra, the temperature of the standard sample and the sample to be tested is controlled to be between -5℃ and 15℃.

5. The test method according to any one of claims 1-4, characterized in that, Before, during, and after spectral acquisition, the sample chamber of the spectrometer is continuously or intermittently purged with dry gas.

6. The test method according to any one of claims 1-5, characterized in that, Near-infrared spectra were acquired using absorbance data mode, covering a spectral range of 1250 nm to 1950 nm.

7. The test method according to any one of claims 1-6, characterized in that, In step (2), when establishing the quantitative analysis model, the spectral data used is selected from one of the following methods: a) Use absorbance data across all wavelengths collected; b) Select absorbance data within one or more wavelength ranges; c) Select absorbance data at multiple discrete characteristic wavelength points.

8. The test method according to any one of claims 1-7, characterized in that, In step (2), the near-infrared spectral set is preprocessed first, and then the preprocessed near-infrared spectral data containing absorbance at multiple wavelengths is correlated with the corresponding water content value through a multivariate correction algorithm to construct a quantitative detection model. Preferably, the preprocessing method is selected from one or more of the following: baseline correction, standardization, mean centering, first derivative, second derivative, multivariate scattering correction, standard normal variable transformation, detrending, and Savitsky-Golay smoothing; Preferably, the multivariate correction algorithm is selected from one or more of the following: multivariate linear regression, principal component regression, and partial least squares.

9. A near-infrared spectroscopy analysis system for implementing the test method according to any one of claims 1-8, characterized in that, The system includes: Near-infrared spectrometer, used to collect near-infrared spectra of standard samples and samples to be tested; Temperature control device, used to adjust and stabilize the temperature of the sample during spectral acquisition; The computing processing unit is configured as follows: Store the standard spectral dataset and the known content of each component; A multivariate correction algorithm is executed to establish the quantitative detection model; The spectrum of the sample to be tested is received, and the equivalent water content is calculated and output using the quantitative detection model.

10. A non-transitory computer-readable storage medium storing a computer program, characterized in that, When executed by a processor, the program is configured to implement a method for testing the equivalent water content in a nitro oxidant as described in any one of claims 1-8.

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