Infrared transmission tabletting sample preparation method for strong-absorptivity black material and tabletting slice

Abstract

The invention relates to the technical field of material testing, in particular to an infrared transmission tabletting sample preparation method for a strong-absorptivity black material and an obtained tabletting slice. The method comprises the following steps: grinding dry potassium bromide, pressing into a transparent background sheet, and immediately collecting a background spectrum; and co-grinding 0.02-0.4 part by mass of the dried black sample and 100 parts by mass of dried potassium bromide, tabletting to obtain a gray light-transmitting sheet, and immediately measuring. The whole process is operated under an infrared baking lamp and in an environment with the humidity of less than or equal to 30%, tabletting parameters are strictly controlled, and'measurement while pressing 'is realized. Water peak interference can be effectively eliminated, the light transmittance, the signal-to-noise ratio and the baseline stability are remarkably improved, and the method is suitable for high-quality infrared characterization of high-absorptivity samples such as carbon materials, asphalt and ferrous metal materials.

Description

Technical Field

[0001] This invention belongs to the field of analytical testing technology, and specifically relates to a method for preparing infrared transmission pellets of strongly absorbing black materials, as well as the pellet sheet. Background Technology

[0002] Fourier transform infrared spectroscopy is an important analytical technique for characterizing the chemical structure and functional groups of materials. The KBr pellet method is one of the most commonly used methods for preparing solid samples. However, when this method is used to test black or dark-colored inorganic powder samples, significant technical bottlenecks exist: 1. Inorganic substances have weaker peak intensity and their peak positions are more easily affected by environmental factors, making it more difficult to extract peaks.

[0003] 2. Black or dark-colored samples have strong absorption and poor signal-to-noise ratio. When using conventional sample preparation methods, the baseline is prone to tilting, and characteristic peaks may even become unidentifiable or inverted peaks may appear. However, blindly reducing the sample amount may result in uneven sample distribution, weaker sample peak intensities, and poorer spectral quality.

[0004] 3. KBr has strong hygroscopic properties. During the grinding and mixing process, KBr absorbs moisture from the air, causing it to condense at 3400 cm⁻¹. -1 and 1640cm -1 The presence of water absorption peaks can interfere with the identification of hydroxyl and other functional groups in the sample.

[0005] Therefore, conventional proportions and operations are difficult to apply directly to the determination of infrared spectra of black powders. There is an urgent need for a pellet preparation and testing method specifically designed for such samples and capable of obtaining high-quality, high signal-to-noise ratio infrared spectra.

[0006] Existing technology: Modern infrared spectroscopy is widely used for structural analysis of organic compounds, polymers, and high molecular weight materials. A common method involves thoroughly mixing and grinding 1-2 mg of sample with 100-200 mg of potassium bromide powder. The ground mixture is then evenly placed into a black spacer between the top and bottom molds of a die. The die is then placed in a hydraulic press under appropriate pressure (8 MPa) to obtain a transparent or uniformly translucent disc of uniform thickness. Finally, the pressed disc is placed into a sample chamber for testing.

[0007] Technical problems with existing technologies: Tableting methods are subject to many interfering factors: (1) The sample is easily exposed to moisture in the air during the mixing and grinding process with potassium bromide, which will interfere with the analysis of samples containing NH and OH groups.

[0008] (2) The sample concentration and test thickness should be appropriate. If it is too dilute or too thin, some weak peaks may not appear; if it is too concentrated or too thick, flat peaks may appear, the baseline may shift and the peak position cannot be determined.

[0009] (3) When the sample color is too dark, the light transmittance of the sample is poor and the intensity of the absorption peak is very weak. Summary of the Invention

[0010] Based on the above technical problems, the purpose of this invention is to provide an infrared transmission compression sample preparation method suitable for highly absorbent black inorganic powder materials and the obtained compressed sheet. This method effectively suppresses the generation of moisture interference peaks by systematically controlling the drying degree of potassium bromide, accurately setting the mass ratio of sample to potassium bromide, limiting the physical thickness after compression molding, and completing key operation steps in a low humidity environment. This avoids baseline drift, peak inversion, or weak peak loss caused by excessively high or low sample concentrations, and ultimately obtains a high-quality Fourier transform infrared spectrum with a stable baseline, clearly distinguishable characteristic absorption peaks, and a significantly improved signal-to-noise ratio.

[0011] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: A method for preparing infrared transmission pellets for highly absorbent black materials, characterized by including a background acquisition step and a sample pellet preparation step; Background data collection: Using an analytical balance with an accuracy of not less than one ten-thousandth of a gram, weigh a predetermined mass of pretreated potassium bromide powder, place it in an agate mortar and grind it thoroughly. The grinding time is controlled within a preset working range to obtain potassium bromide fine powder with uniform particle size and good flowability. The ground potassium bromide powder is transferred to the upper surface of the lower mold core of a clean and dry tableting mold. The mold is then slightly vibrated to form a flat and gapless accumulation layer of powder on the surface of the lower mold core. The upper mold core is then vertically aligned and placed over the accumulation layer, ensuring that the upper mold core and the lower mold core are coaxially aligned. The assembled tableting mold is then placed into the working chamber of the hydraulic tableting machine and held at a preset pressure value for a predetermined time. After the pressure holding is completed, the hydraulic system pressure is released slowly, the upper mold groove and the lower mold groove are removed in sequence, the transparent sheet formed by pure potassium bromide is taken out, and the background spectrum is collected immediately in the sample chamber of the Fourier transform infrared spectrometer after demolding is completed. Sample tablet preparation: Using the analytical balance, weigh the same mass of pretreated potassium bromide powder and dry black powder sample within the predetermined value range as in the background acquisition step, and place them together in another clean agate mortar for mixing and grinding. The grinding time is consistent with that in the background acquisition step, so that the black powder can be dispersed at the molecular level and evenly distributed in the potassium bromide matrix. The resulting mixed powder is transferred to the upper surface of the lower mold core of another clean and dry tableting mold. The mixed powder is then subjected to slight vibration to form a dense and flat accumulation layer. The upper mold core is then placed on top to ensure a seamless fit between the upper and lower mold cores. The mold is then placed in the same hydraulic tableting machine and pressed into shape under the same preset pressure value and holding time as in the background acquisition step. After pressing, the pressure is slowly released and the mold assembly is disassembled in the same way to obtain a semi-transparent gray composite pressed sheet. Immediately after demolding, the sheet is loaded into the sample chamber of an infrared spectrometer for sample spectral measurement. Preferably, the potassium bromide powder is placed in a constant temperature drying device before use and dried continuously at a predetermined temperature for more than a predetermined time to fully remove the environmental moisture adsorbed on its crystal surface and internal pores. Preferably, the powder transfer, mold assembly and tableting operations in the background collection step and the sample tableting step are all carried out in a local heating atmosphere. The local heating atmosphere is provided by an infrared radiation heat source, and its effective area covers the entire operating table surface to maintain the relative humidity in the operating space below a preset threshold and prevent potassium bromide and the sample from reabsorbing moisture during exposure. Preferably, the black powder sample is placed in another constant temperature drying device before mixing and dried for more than a predetermined time in a predetermined temperature range below the potassium bromide drying temperature to remove the moisture physically adsorbed on the surface of the sample particles, while avoiding thermal decomposition or phase change of the sample structure due to high temperature. Preferably, the structure of the tableting mold is designed such that the physical thickness of the tablet formed under the preset pressure value and pressure holding conditions is limited to a range of ± preset tolerance with reference thickness as the center. The reference thickness is predetermined based on the light absorption characteristics of the black sample to ensure that the infrared beam does not attenuate excessively and cause signal loss when penetrating the tablet, nor does it fail to reflect characteristic absorption due to excessive transmittance. Preferably, the upper and lower cores of the tableting mold are both made of high-hardness stainless steel, and their contact surfaces are mirror-polished to reduce powder adhesion and ensure that the tableting surface is smooth and flat. The outer wall of the mold is provided with an annular sealing groove, and an elastic sealing ring is embedded during assembly so that the upper and lower cores are closed to form a partially sealed cavity, further isolating external moisture from intrusion. Preferably, the pressure control system of the hydraulic tablet press is equipped with a digital pressure sensor and a closed-loop feedback module, which can monitor and dynamically adjust the load applied to the mold in real time during the pressing process, so that the actual pressure fluctuation range does not exceed ± a preset percentage of the preset pressure value, thereby ensuring that the density and optical uniformity of different batches of tablets are highly consistent. Preferably, the agate mortar and pestle are cleaned and dried with anhydrous ethanol before and after each use to avoid cross-contamination and the introduction of residual moisture; during the grinding process, a unidirectional rotation with intermittent light pressure is used to prevent local overheating that could lead to deliquescence of potassium bromide or oxidation of the sample. Preferably, the analytical balance is placed on a shockproof platform and equipped with a transparent windproof cover. The weighing operation is carried out with the windproof cover closed to eliminate the influence of air flow on the weighing accuracy of trace samples. Preferably, the time interval between background acquisition and sample measurement of the Fourier transform infrared spectrometer does not exceed a preset aging window, and the desiccant inside the instrument is in an effective working state to ensure that the environmental conditions of the optical system are stable during the two measurements. Preferably, the composite compressed sheet is verified for thickness using a non-contact thickness measuring device after demolding. If the measured thickness deviates from the preset thickness range, the compressed sheet is discarded and remade. Preferably, the ratio of the mass of the black powder sample to the mass of the potassium bromide powder is strictly limited to a predetermined ratio range optimized for highly absorbent inorganic materials. This range is determined through preliminary experiments to avoid light absorption saturation and baseline tilting caused by excessive sample, and to prevent the characteristic peak intensity from falling below the instrument detection limit due to insufficient sample. Preferably, the composite sheet after compression molding has no cracks, no delamination, and no obvious color difference areas at the edge, and exhibits a uniform gray distribution, indicating that the sample is well dispersed in the potassium bromide matrix and there is no abnormal stress concentration during the compression process. Preferably, the background spectrum and the sample spectrum are acquired using the same resolution, number of scans, and aperture settings to ensure data comparability; Preferably, the tableting mold is disassembled and cleaned immediately after each use. It is then cleaned with deionized water and acetone alternately using an ultrasonic cleaner and dried for later use to prevent residual samples or potassium bromide crystals from clogging the mold gap. Preferably, the infrared lamp power of the local heating atmosphere is adjustable, and its irradiation intensity is adjusted in real time according to the ambient temperature and humidity, so that the surface temperature of the operating area is maintained at a level slightly higher than the ambient dew point temperature, thereby effectively suppressing the formation of condensate without causing thermal damage to the sample. Preferably, the constant temperature drying equipment is equipped with a forced convection fan to ensure uniform temperature distribution within the cavity and that the temperature difference at each location does not exceed the preset temperature control accuracy. Preferably, the black powder sample is placed in a desiccator to cool to room temperature after drying before being weighed, to avoid the hot sample absorbing moisture from the air during the weighing process. Preferably, the particle size of the potassium bromide powder is controlled within a preset particle size range after grinding. Overly large particles will cause uneven tableting, while overly fine particles will easily agglomerate and affect dispersibility. Preferably, the working platform of the tablet press is precisely calibrated to ensure that the upper and lower mold cores are subjected to uniform force during the pressing process, and to avoid wedge-shaped or locally thin areas in the tablet press. Preferably, when the composite tablet is removed from the mold, ceramic tweezers are used to hold the edges to avoid contamination from finger contact or the introduction of grease interference. Preferably, the pure potassium bromide pellets used for background collection and the sample pellets are highly consistent in terms of geometric dimensions, surface finish and optical transmittance, so as to eliminate systematic errors introduced by substrate differences. Beneficial effects: Compared with existing technologies, this invention has the following advantages: By independently drying potassium bromide and the black sample and limiting their moisture content before mixing, the path to the generation of moisture interference peaks is cut off at the source; by completing key operation steps under a local heating atmosphere, a temporary low-humidity microenvironment is constructed, effectively blocking secondary adsorption of ambient moisture during operation; by limiting the mass ratio of the sample to potassium bromide within a predetermined ratio range optimized for highly absorbent black inorganic materials, and combining this with precise control of the physical thickness of the compressed tablet, the infrared light is positioned at the optimal temperature when penetrating the sample. The optimal absorption range avoids baseline tilting and inverted peaks caused by excessively high concentrations, while overcoming the problem of missing characteristic peaks caused by excessively low concentrations. By standardizing the preparation process parameters of background and sample films, including pressure, holding time, mold condition, and operating techniques, the repeatability and reliability of the test results are significantly improved. Through the coordinated operation of each step in the entire method, the final infrared spectrum has a stable baseline, no obvious water vapor interference peaks, clearly distinguishable characteristic absorption peaks, and a high signal-to-noise ratio, providing accurate and reliable technical support for the identification of functional groups and structural analysis of black inorganic powder materials. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 The Fe3O4 spectrum measured by the method of this invention; Figure 2 Fe3O4 spectrum measured with potassium bromide:sample amount = 100:1; Figure 3 This is the Fe3O4 spectrum measured under conditions where potassium bromide was not dried and had a high moisture content; Figure 4 This is the Fe3O4 spectrum measured when the sample was not dried and had a high moisture content; Figure 5 The spectrum of Fe3O4 obtained when the tablet thickness is less than 0.5 mm; Figure 6 The spectrum of Fe3O4 obtained when the tablet thickness is greater than 1.5 mm; Figure 7 The Fe3O4 spectrum was obtained when the ambient humidity was greater than 60%. Figure 8 The carbon black spectrum measured by the method of this invention; Figure 9 The asphalt spectrum measured by the method of this invention; Figure 10 The molybdenum disulfide spectrum measured by the method of this invention; Figure 11 The lithium iron phosphate spectrum measured by the method of this invention; Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0015] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0017] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0018] The raw materials used in the examples were sourced from (Fe3O4: MCC New Materials Technology Co., Ltd.; Molybdenum disulfide: Suzhou Yuante New Materials Technology Co., Ltd.; Asphalt: Guangzhou Zhuguang New Energy Technology Co., Ltd.; Lithium iron phosphate: Defang Nano); Carbon black: China National Institute of Metrology; and other experimental equipment and samples were sourced from (Fourier transform infrared spectrometer: ThermoScientific Nicolet Summit X; Hydraulic press: Shanghai Yixiang Instrument Co., Ltd.; Infrared lamp: ZHDK10).

[0019] Example 1: Fe3O4 Sample Preparation and Testing (Benchmark Protocol) Implementation plan: Potassium bromide pretreatment: Dry at 120℃ for 4 hours, then cool to room temperature for later use; Sample pretreatment: The Fe3O4 sample was dried at 80℃ for 2 hours and then cooled to room temperature for later use. Background film preparation: Weigh 200.0 mg of dried KBr and place it in an agate mortar. Under irradiation with a 250 W infrared lamp (irradiation distance 12 cm, operating area RH=25%), grind for 1.5 min using unidirectional rotation and intermittent light pressure to obtain fine powder with a particle size of 2-5 μm. Transfer it to the lower core of a clean and dried tableting mold, tap it lightly to form a flat accumulation layer, cover it with the upper core and insert a fluororubber sealing ring, place it in a tablet press and apply a pressure of 8.0 MPa for 2 min, and release the pressure at a rate of 0.5 MPa / s. Use ceramic tweezers to pick up the transparent thin film and immediately collect the background spectrum. Sample preparation: Weigh 200.0 mg of dry KBr and 0.4 mg of dry Fe3O4 sample, place them in another clean agate mortar, and grind them together for 1.5 min under the same infrared heating atmosphere; transfer them to another set of molds of the same specifications, and press them into tablets with the same pressure, holding time and depressurization rate as the background tablets to obtain a translucent gray composite sheet with a thickness of 0.80±0.03 mm, and immediately test the sample spectrum.

[0020] Test data: Tablet appearance: No cracks or delamination at the edges, uniform gray scale; Infrared spectrum: 3400cm -1 With 1640cm -1 No obvious water peak was observed at 580 cm⁻¹, and Fe₃O₄ showed a peak at 580 cm⁻¹. -1 The characteristic absorption peaks are clear; Signal-to-noise ratio (SNR): 42.3; Thickness deviation: 0.802mm, which meets the requirement of 0.80±0.05mm.

[0021] Example 2: MoS2 Sample Preparation and Testing (Compatibility with Different Samples) Implementation plan: Potassium bromide pretreatment: Dry at 110℃ for 5 hours, then cool to room temperature for later use; Sample pretreatment: MoS2 samples were dried at 70℃ for 3 hours and then cooled to room temperature for later use. Background sheet preparation: Same as in Example 1 (infrared lamp power 220W, operating area RH=28%, grinding for 1min, pressure 8.0MPa, holding pressure for 2min, depressurization rate 0.4MPa / s). Sample preparation: Weigh 200.0 mg of dry KBr and 0.4 mg of dry MoS2 sample, place them in another clean agate mortar, and grind them together for 1 min under the same infrared heating atmosphere; transfer them to another mold and press them into tablets with the same parameters to obtain a semi-transparent gray tablet with a thickness of 0.81 ± 0.04 mm, and test immediately.

[0022] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, 470 cm⁻¹ -1 The peaks at (Mo-S bond stretching vibration) and (Mo-S bond bending vibration) are symmetrical, and the baseline is not tilted; Signal-to-noise ratio (SNR): 38.7; Thickness deviation: 0.808mm, which meets the requirements.

[0023] Example 3: LiFePO4 Sample Preparation and Testing (Thickness and Mold Optimization) Implementation plan: Potassium bromide pretreatment: Dry at 130℃ for 3 hours, then cool to room temperature for later use; Sample pretreatment: The LiFePO4 sample was dried at 60℃ for 4 hours and then cooled to room temperature before use. Background sheet preparation: Same as in Example 1 (infrared lamp power 280W, operating area RH=26%, grinding for 2min, pressure 8.0MPa, holding pressure for 2min, depressurization rate 0.6MPa / s). Sample preparation: Weigh 200.0 mg of dry KBr and 0.4 mg of dry LiFePO4 sample, place them in another clean agate mortar, and grind them together for 2 min under the same infrared heating atmosphere; transfer them to a mold with a fluororubber sealing ring, press them into tablets with the same parameters, and obtain a semi-transparent gray sheet with a thickness of 0.85±0.02 mm, and test immediately.

[0024] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: free from moisture interference, 1050 cm⁻¹ -1 The strong absorption peak at the (PO bond stretching vibration) is clear; Signal-to-noise ratio (SNR): 45.1; Thickness deviation: 0.849mm, which meets the requirement of 0.85±0.05mm.

[0025] Example 4: High-proportion compatibility test of Fe3O4 samples Implementation plan: Pretreatment conditions: Same as in Example 1 (KBr dried at 120℃ for 4 hours, Fe3O4 dried at 80℃ for 2 hours); Background film preparation: Same as in Example 1; Sample preparation: Weigh 200.0 mg of dry KBr and 0.8 mg of dry Fe3O4 sample, and perform the remaining operations as in Example 1. The tablet thickness is 0.80 ± 0.04 mm.

[0026] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, 580 cm⁻¹ -1 The peak is slightly flat at the top, and the baseline is slightly upward. Signal-to-noise ratio (SNR): 31.2; Thickness deviation: 0.805mm, which meets the requirements.

[0027] Example 5: Low-proportion compatibility test of Fe3O4 samples Implementation plan: Pretreatment conditions: Same as in Example 1; Background film preparation: Same as in Example 1; Sample preparation: Weigh 200.0 mg of dry KBr and 0.04 mg of dry Fe3O4 sample, and perform the remaining operations as in Example 1. The tablet thickness is 0.80 ± 0.03 mm.

[0028] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, 580 cm⁻¹ -1 The peak intensity is weakened but still clearly identifiable; Signal-to-noise ratio (SNR): 29.8; Thickness deviation: 0.798mm, which meets the requirements.

[0029] Example 6: Low Pressure Parameter Adaptability Test Implementation plan: Pretreatment conditions: Same as in Example 1 (KBr dried at 120℃ for 4 hours, Fe3O4 dried at 80℃ for 2 hours); Background tablet preparation: Weigh 200.0 mg of dry KBr, grind it for 1.5 min under infrared lamp irradiation, compress it at a pressure of 7.0 MPa, hold it at the pressure for 3 min, and release the pressure at a rate of 0.3 MPa / s. The rest is the same as in Example 1. Sample preparation: Weigh 200.0 mg of dry KBr and 0.2 mg of dry Fe3O4 sample, grind them together for 1.5 min, and compress them into tablets with the same pressure, holding time and depressurization rate as the background tablets, with a thickness of 0.81 ± 0.04 mm.

[0030] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, 580 cm⁻¹ -1 The characteristic peaks are clear; Signal-to-noise ratio (SNR): 39.5; Thickness deviation: 0.809mm, which meets the requirements.

[0031] Example 7: High Pressure Parameter Adaptability Test Implementation plan: Pretreatment conditions: Same as in Example 1; Background tablet preparation: Weigh 200.0 mg of dry KBr, grind it for 1.5 min under infrared lamp irradiation, compress it at a pressure of 9.0 MPa, hold it at the pressure for 1 min, and release the pressure at a rate of 0.8 MPa / s. The rest is the same as in Example 1. Sample preparation: Weigh 200.0 mg of dry KBr and 0.1 mg of dry Fe3O4 sample, grind them together for 1.5 min, and press them into tablets with the same parameters as the background tablets, with a thickness of 0.79 ± 0.03 mm.

[0032] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, 580 cm⁻¹ -1 The characteristic peaks are clear; Signal-to-noise ratio (SNR): 37.8; Thickness deviation: 0.792mm, which meets the requirements.

[0033] Example 8: Compatibility Test of 316L Stainless Steel Mold Implementation plan: Pretreatment conditions: Same as in Example 1; Mold selection: 316L stainless steel tablet mold (contact surface Ra≤0.05μm, with annular sealing groove and fluororubber sealing ring); Background and sample preparation: Same as in Example 1, sample thickness 0.80±0.04mm.

[0034] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, 580 cm⁻¹ -1 The characteristic peaks are clear; Signal-to-noise ratio (SNR): 41.7; Thickness deviation: 0.803mm, which meets the requirements.

[0035] Example 9: Compatibility Test of Isopropanol for Cleaning Mortars Implementation plan: Pretreatment conditions: Same as in Example 1; Mortar cleaning: The agate mortar and pestle are cleaned with isopropyl alcohol before and after use, and then dried for later use. Background and sample preparation: Same as in Example 1, sample thickness 0.80±0.03mm.

[0036] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No clutter peaks, no obvious water peaks, 580 cm⁻¹ -1 The characteristic peaks are clear; Signal-to-noise ratio (SNR): 40.9; Thickness deviation: 0.801mm, which meets the requirements.

[0037] Example 10: High Humidity Environment Boundary Condition Test Implementation plan: Pretreatment conditions: Same as in Example 1; Operating environment: Under infrared lamp irradiation, the relative humidity of the operating area is controlled at 30%; Background and sample preparation: Same as in Example 1, sample thickness 0.81±0.04mm.

[0038] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: 3400cm -1 With 1640cm -1 The presence of a slight water peak (peak height < 3% transmittance) does not affect the identification of characteristic peaks; Signal-to-noise ratio (SNR): 36.2; Thickness deviation: 0.807mm, which meets the requirements.

[0039] Comparative Example 1: No drying treatment + no low-humidity environment (conventional method) Implementation plan: Commercially available KBr and Fe3O4 samples were used directly without undergoing drying treatment with KBr and Fe3O4. Operating environment: no infrared heat lamp irradiation, 25℃, RH=50%; Weigh 200.0 mg of undried KBr and 2.0 mg of undried Fe3O4 sample, and grind and mix them at room temperature for 5 min; The tableting pressure was 8.0 MPa, the pressure was held for 2 minutes, the pressure release rate was 0.5 MPa / s, and the tablet was placed for 5 minutes after demolding before testing.

[0040] Test data: Tablet appearance: uneven grayness, with tiny cracks at the edges; Infrared spectrum: 3400cm -1 With 1640cm -1 A significant water peak (peak height ≥ 15% transmittance) is located at 580cm. -1 The peak is inverted; Signal-to-noise ratio (SNR): 18.6; Thickness deviation: 0.82mm, but due to water peak and inverted peak issues, it cannot be used for structural analysis.

[0041] Comparative Example 2: Low Sample Size Testing Using Conventional Methods Implementation plan: No KBr and Fe3O4 drying treatment was performed; the operating environment was 25℃ and RH=50% (without infrared lamps). Weigh 200.0 mg of undried KBr and 0.5 mg of undried Fe3O4 sample, and grind and mix them at room temperature for 5 min; The tableting pressure was 8.0 MPa, the pressure was held for 2 minutes, the pressure release rate was 0.5 MPa / s, and the tablet was placed for 5 minutes after demolding before testing.

[0042] Test data: Tablet appearance: uneven grayness, no obvious cracks; Infrared spectrum: 3400cm -1 With 1640cm -1 A significant water peak, 580cm -1 The intensity of the characteristic peak is below the detection limit, and the spectrum approximates background noise. Signal-to-noise ratio (SNR): 15.3; Thickness deviation: 0.81mm, characteristic peaks cannot be identified.

[0043] Comparative Example 3: High Sample Quantity Testing Using Conventional Methods Implementation plan: No KBr and Fe3O4 drying treatment was performed; the operating environment was 25℃ and RH=50% (without infrared lamps). Weigh 200.0 mg of undried KBr and 5.0 mg of undried Fe3O4 sample, and grind and mix them at room temperature for 5 min; The tableting pressure was 8.0 MPa, the pressure was held for 2 minutes, the pressure release rate was 0.5 MPa / s, and the test was conducted immediately after demolding.

[0044] Test data: Tablet appearance: Opaque, dark black, with layered edges; Infrared spectrum: Infrared light cannot penetrate, and the instrument reports an error "signal overload"; Signal-to-noise ratio (SNR): No valid data; Thickness deviation: 0.83mm, test cannot be completed.

[0045] Comparative Example 4: The drying temperature of KBr+ was inconsistent between different batches. Implementation plan: The background film was dried with KBr at 100℃ for 4 hours. The sample slides were dried with KBr at 140℃ for 4 hours. Fe3O4 samples were dried at 80℃ for 2 hours, with the operating environment (infrared lamp, RH=25%) and tableting parameters the same as in Example 1. Test immediately after demolding.

[0046] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: No obvious water peak, but the baseline shows a systematic shift, and two spurious peaks appear in the difference spectrum (2800 cm⁻¹). -1 With 1450cm -1 (place); Signal-to-noise ratio (SNR): 25.7; Thickness deviation: 0.80mm, spurious peak interference structure analysis.

[0047] Comparative Example 5: Excessive grinding time + localized temperature rise Implementation plan: KBr was dried at 120℃ for 4 hours, and Fe3O4 was dried at 80℃ for 2 hours, with the same operating environment as in Example 1. Background film preparation: KBr grinding for 15 min, other parameters are the same as in Example 1; Sample preparation: KBr and Fe3O4 were co-ground for 15 min, and the other parameters were the same as in Example 1; Test immediately after demolding.

[0048] Test data: Tablet appearance: The surface has tiny droplet marks and uneven grayness; Infrared spectrum: 3400cm -1 With 1640cm -1 Slight water peak (peak height ≈ 8% transmittance), 580cm -1 The peak intensity decreases; Signal-to-noise ratio (SNR): 24.3; Thickness deviation: 0.80mm, water peak interference characteristic peak judgment.

[0049] Comparative Example 6: Not "Instant Pressure Testing" + Secondary Moisture Absorption Implementation plan: KBr was dried at 120℃ for 4 hours, and Fe3O4 was dried at 80℃ for 2 hours. The operating environment and tableting parameters were the same as in Example 1. After collecting the background image, let it sit for 15 minutes before testing the sample image. The sample was placed for 15 minutes after demolding before testing.

[0050] Test data: Tablet appearance: No cracks, no delamination, uniform gray scale; Infrared spectrum: 3400cm -1 The peak intensity at 1640 cm⁻¹ is 3.2 times that of Example 1 (peak height ≈ 12% transmittance). -1 The water level peak is significant; Signal-to-noise ratio (SNR): 21.8; Thickness deviation: 0.81 mm, water peaks severely interfere with the intrinsic signal of the sample.

[0051] In practice, following the preparation process of Example 1, 200.0 mg of potassium bromide powder, dried at 120°C for 4 hours, was placed in a clean agate mortar. The mortar was placed within the irradiation range of an infrared lamp, maintaining an appropriate distance between the infrared heat source and the grinding container to create a localized low-humidity environment (relative humidity <30% RH). This environment inhibits the adsorption of water molecules from the air onto the KBr surface through infrared thermal radiation. Grinding was performed for 5 minutes under these conditions to refine the KBr particles to a range of 2-5 μm. This particle size ensures good flowability for uniform spreading while avoiding excessive fineness that could lead to agglomeration or increased moisture absorption. After grinding, the resulting fine powder was transferred to the upper surface of the lower mold core of a stainless steel tableting mold that had been ultrasonically cleaned with acetone and dried. The mold was gently tapped to allow the powder to settle naturally and spread into a uniform thin layer. This process relied on the low adhesion characteristics provided by the surface roughness Ra ≤ 0.05 μm of the lower mold core (as described in Example 3), ensuring that the powder distribution was free of voids or accumulation.

[0052] Subsequently, the upper mold core was vertically inserted into the outer wall of the lower mold core, and the two were aligned coaxially before being placed in the center of the hydraulic press platform. The hydraulic press applied a pressure of 8.0 MPa and held it for 2 minutes. This pressure value has been experimentally verified to allow KBr particles to densely bond under plastic deformation, forming an optically uniform transparent sheet. After holding the pressure, the pressure was slowly released at a rate of 0.5 MPa / s to avoid uneven internal stress release due to excessively rapid pressure release, which could lead to microcracks or delamination. Immediately after demolding, the obtained pure KBr sheet was picked up with ceramic tweezers and placed in the sample chamber of a Fourier transform infrared spectrometer to collect the background spectrum. This "immediate" operation was intended to prevent secondary moisture absorption due to exposure to air after demolding. As shown in Comparative Example 6, a delay of 10 minutes caused a 3400 cm⁻¹ precipitate. -1The intensity of the water peak increased significantly.

[0053] During the sample preparation stage, 0.4 mg of iron(III) oxide sample dried at 80℃ for 2 h was placed together with 200.0 mg of dried KBr from the same batch in another clean agate mortar and ground together for 5 min under the same infrared radiation heat source. This simultaneous mixing and refining process not only ensured that the black sample particles were fully coated by the KBr matrix, but also maintained a low-humidity environment with the help of the infrared thermal field, preventing the introduction of moisture during the mixing process. Since the black sample has strong infrared absorption characteristics, if it is mixed directly at the conventional 1:100 ratio, it will result in too low transmittance, as shown in Comparative Example 3, where "signal overload" occurs. However, this invention controls the sample amount in the range of 0.04-0.8 mg (corresponding to 200 mg of KBr) and controls the tablet thickness at 0.80±0.05 mm (as shown in Examples 1, 4, and 5), so that the infrared beam is in the linear response region of Beer-Lambert's law when penetrating the composite tablet, thereby avoiding the phenomenon of inverted peaks or flat tops. The pressing process is completely consistent with the background film, ensuring that the two films are highly matched in density, thickness and optical properties, eliminating baseline shift caused by substrate differences. As shown in Comparative Example 4, different batches or drying conditions of KBr can cause spurious peaks in the difference spectrum.

[0054] Furthermore, the spatial layout of the infrared radiation heat source covers the entire operating surface, and its thermal radiation creates a microenvironment with a temperature slightly higher than the ambient dew point around the mortar and mold, effectively suppressing condensation and preventing thermal decomposition caused by direct heating of the sample. A fluororubber sealing ring (as described in Example 3) is embedded in the annular groove on the outer wall of the mold, forming a locally sealed cavity when the upper and lower mold cores are closed, further isolating external moisture from intruding into the pressing process. The resulting composite sheet after demolding is translucent gray, indicating that the sample is uniformly dispersed in the KBr matrix without local enrichment or agglomeration; this uniformity is a prerequisite for obtaining a stable baseline.

[0055] In summary, this invention, through the synergistic effect of multiple aspects such as drying pretreatment, local low-humidity operating environment, precise proportioning control, thickness limitation, and mold sealing design, solves the problem of poor spectral quality caused by strong absorption, easy hygroscopicity, and uneven dispersion of black inorganic powders in KBr tableting. This allows for the detection of previously difficult-to-detect weak characteristic peaks (such as Fe3O4 at 580 cm⁻¹). -1 MoS2 at 470cm -1 The signal-to-noise ratio is improved to over 29.8, which meets the requirements of structural analysis. All content not described in detail in this specification is prior art known to those skilled in the art, and the equipment model used is not specifically limited; conventional instruments can be used to achieve this technical solution. The above description is only a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing infrared transmission pellets of strongly absorbing black materials, characterized in that, The method includes the following steps: (1) Background acquisition: Weigh 100 parts by weight of dry potassium bromide, grind it into powder in an agate mortar, transfer it to the surface of the lower mold core of a clean tableting mold, vibrate to flatten the powder and cover it with the upper mold core, put it into the tablet press, apply pressure and hold the pressure, release the pressure and demold to obtain transparent potassium bromide sheets. Start timing from the time the tablet demolding is completed, and within 60 seconds, use ceramic tweezers to pick up and transfer the sample chamber of the Fourier transform infrared spectrometer and start the background spectrum acquisition program. (2) Sample tablet preparation: Weigh 100 parts by weight of dry potassium bromide and 0.02-0.4 parts by weight of the dry sample to be tested, grind them in an agate mortar until they are mixed into a uniform powder, transfer them to the surface of the lower mold core of a clean tablet mold, vibrate to flatten the powder and cover it with the upper mold core, put it into the tablet press, apply pressure and hold the pressure, release the pressure and demold to obtain a gray transparent potassium bromide sheet. Start timing from the time the tablet demolding is completed, and within 60 seconds, use ceramic tweezers to pick up and transfer the sample to the sample chamber of the Fourier transform infrared spectrometer and start the background spectrum acquisition program.

2. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 1, characterized in that, The specific process for background collection is as follows: Using an analytical balance with an accuracy of not less than 0.1 mg, weigh potassium bromide powder that has been dried at 100-120℃ for 4-8 hours. Place the powder in an agate mortar and grind it for 1-2 minutes under infrared radiation heat source irradiation to obtain fine potassium bromide powder with an average particle size D50 of 2-5 μm. Transfer the obtained fine potassium bromide powder to the upper surface of the lower mold core of a clean and dry tableting mold, and gently tap it to form a flat accumulation layer of powder. Vertically insert the upper mold core into the outer wall of the lower mold core and align them coaxially. Place the assembled tableting mold in the working chamber of a hydraulic tablet press, maintain pressure at 7-9 MPa for 1-3 minutes, and then slowly release the pressure at a rate of 0.3-0.8 MPa / s. Sequentially remove the upper and lower mold slots, use ceramic tweezers to pick up the obtained transparent potassium bromide sheet, and place it into the sample chamber of a Fourier transform infrared spectrometer to collect the background spectrum.

3. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 2, characterized in that, The specific process for preparing the sample tablet is as follows: using the analytical balance, weigh the potassium bromide powder that has been dried at 100-120℃ for 4-8 hours and the black powder sample that has been dried at 60-80℃ for 2-4 hours, and place them together in another clean agate mortar and grind them together for 1-2 minutes under infrared radiation heat source irradiation. Transfer the resulting mixed powder to the upper surface of the lower core of another clean and dry tableting mold, and form a flat accumulation layer by tapping; cover with the upper core and align coaxially; place the mold in the same hydraulic tableting machine, hold the pressure at 7-9MPa for 1-3 minutes, and then slowly release the pressure at a rate of 0.3-0.8MPa / s. The mold was disassembled, and the resulting translucent gray composite sheet was picked up with ceramic tweezers and placed into the sample chamber of the Fourier transform infrared spectrometer for sample spectral measurement.

4. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 2 or 3, characterized in that, The background acquisition step and the powder transfer, mold assembly and tableting operations in the sample tableting process are all carried out in a local heating atmosphere provided by an infrared radiation heat source, and the relative humidity of the operation area is less than 30%RH.

5. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 2 or 3, characterized in that, The tableting die forms a tablet sheet under a pressure of 8.0 MPa and a holding pressure of 2 minutes. The tableting die also includes an annular height limiting washer with a thickness of 0.80 ± 0.02 mm, which is assembled between the upper and lower die cores to limit the final thickness of the tablet sheet to 0.80 ± 0.05 mm during the pressing process.

6. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 2 or 3, characterized in that, The upper and lower mold cores of the tablet compression mold are both made of high-hardness stainless steel, and the surface roughness of their contact surfaces Ra≤0.05μm. The outer wall of the mold is provided with an annular sealing groove, and a fluororubber sealing ring is embedded during assembly.

7. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 2 or 3, characterized in that, The pressure control system of the hydraulic tablet press is equipped with a digital pressure sensor and a closed-loop feedback module, and the actual pressure fluctuation range does not exceed ±0.2MPa of the set pressure value.

8. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 2 or 3, characterized in that, The agate mortar and pestle are cleaned and dried with anhydrous ethanol before and after each use. During the grinding process, a unidirectional rotation plus intermittent light pressure method is used.

9. The method for preparing infrared transmission pellets of strongly absorbing black materials according to claim 1, characterized in that, The dried sample to be tested is any one of carbon material, MoS2, Fe3O4, and LiFePO4.

10. The compressed sheet obtained by the infrared transmission pressing method for preparing samples of strongly absorbing black materials according to any one of claims 1 to 9, characterized in that, The compressed sheet is semi-transparent gray, with no cracks, delamination, or obvious color difference areas at the edges, and presents a uniform gray distribution overall.

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