Fourier infrared mixed gas calibration device, calibration method and preparation method

Abstract

The invention discloses a Fourier infrared mixed gas calibration device, a calibration method and a preparation method, and belongs to the technical field of Fourier infrared spectrometer calibration. According to the Fourier infrared mixed gas calibration device, stable isolation between calibration gas and the external environment is achieved through direct welding packaging of metal and the diaphragm, component change or concentration fluctuation of the calibration gas caused by invasion of external temperature, humidity and pollutants is avoided, and a long-term stable built-in reference basis is provided for an instrument. And through welding sealing, the risks of gas leakage and light path deviation caused by aging and loosening of the sealing ring are eliminated, and the physical stability and environmental adaptability of the device are remarkably improved. Therefore, the device can provide a constant, reliable and maintenance-free built-in gas scale for the Fourier infrared spectrometer, and the defects of frequent operation and insufficient stability of a traditional external standard gas calibration mode are effectively overcome.

Description

Technical Field

[0001] This application relates to the field of Fourier transform infrared (FTIR) spectrometer calibration technology, and in particular to a Fourier transform infrared mixed gas calibration device, calibration method, and preparation method. Background Technology

[0002] Fourier transform infrared spectroscopy (FTIR) is an analytical method based on the interaction between infrared radiation and molecules. By detecting the absorption characteristics of molecules within a specific wavelength range, it is possible to accurately identify various components and their concentrations in a gas. This technology is widely used in various fields such as engineering air quality, closed and semi-closed chambers, atmospheric pollution control, industrial process control, and scientific research.

[0003] Under different temperature and pressure conditions, Fourier transform infrared (FTIR) gas analyzers can produce inconsistent detection results for the same substance at the same concentration. Calibration is an essential and crucial step to ensure the accuracy and stability of FTIR gas analyzers. Traditional gas calibration methods typically rely on standard gases of known concentrations, adjusting sensitivity and response characteristics by comparing them with instrument measurements. However, after long-term use, due to sensor drift, environmental interference, and issues with the purity of standard gases, the stability of traditional calibration methods often fails to meet practical requirements. Summary of the Invention

[0004] This application provides a Fourier transform infrared mixed gas calibration device, calibration method, and preparation method, which improves the stability of calibration and at least partially solves the above-mentioned technical problems.

[0005] To achieve the above objectives, according to a first aspect of this application, a Fourier transform infrared mixed gas calibration device is provided, comprising: The metal substrate has a through-hole for light transmission; Two windows are configured to transmit infrared light. Each window has a coating structure. The two windows are hermetically welded to the metal substrate through the coating structure and cover both ends of the light-transmitting hole, so as to form a sealed chamber with the metal substrate for containing calibration gas.

[0006] In some embodiments, the metal substrate is Kovar alloy, and the window is a zinc selenide glass sheet.

[0007] In some embodiments, the coating structure is formed in an annular region at the edge of the window sheet for welding to the metal substrate.

[0008] In some embodiments, the width L of the annular region is less than or equal to 1.5 mm.

[0009] In some embodiments, the coating structure includes a first metal layer, a second metal layer, and a third metal layer sequentially stacked on the edge surface of the window sheet, wherein the chemical activity of the first metal layer, the second metal layer, and the third metal layer decreases sequentially.

[0010] In some embodiments, the first metal layer is a titanium layer, the second metal layer is a nickel layer, and the third metal layer is a gold layer, wherein the window is welded to the metal substrate through the gold layer.

[0011] In some embodiments, the thickness of the first metal layer is 0.02 μm to 1 μm, the thickness of the second metal layer is 3 μm to 5 μm, and the thickness of the third metal layer is 1.3 μm to 5 μm.

[0012] In some embodiments, the surface roughness of the coated structure is set to 0.8 μm to 1.6 μm.

[0013] In some embodiments, the light-transmitting hole is configured as a stepped hole, with stepped surfaces formed at both ends of the hole wall, and the window piece is welded to the stepped surfaces through the coating structure.

[0014] In some embodiments, the metal substrate is further provided with an air inlet, which communicates with the sealed chamber; The Fourier transform infrared mixed gas calibration device also includes a sealing plug, which is disposed in the inflation hole and airtightly connected to the metal substrate.

[0015] In some embodiments, the inflation port includes a connecting section and a blocking section, the size of the connecting section being smaller than the size of the blocking section, and the connecting section connecting the sealed chamber and the blocking section; The sealing plug is disposed within the sealing section, and both ends of the sealing plug are provided with sealant.

[0016] In some embodiments, the Fourier transform infrared mixed gas calibration device further includes: The base is equipped with a guide structure; A drive mechanism is mounted on the base, and its drive end is connected to the metal substrate for driving the metal substrate to move along the guide structure.

[0017] According to a second aspect of this application, a laser wavelength calibration method is provided, applied to a Fourier transform infrared mixed gas calibration apparatus as described in any embodiment of the first aspect, the laser wavelength calibration method comprising: Acquire the current calibration spectrum collected by the Fourier transform infrared mixed gas calibration device; Based on the current calibration spectrum, determine the position of the first peak of one or more characteristic absorption peaks of the calibration gas in the sealed chamber under the current state; Based on the first peak position and the pre-stored reference peak position, the current laser wavelength value is determined; wherein, the reference peak position is the second peak position of the corresponding characteristic absorption peak of the calibration gas measured under the reference state; Based on the current laser wavelength value, the horizontal axis of the spectrum is corrected.

[0018] In some embodiments, the current laser wavelength value is determined based on the first peak position and a pre-stored reference peak position using the following formula:

[0019] Where Laser1 is the current laser wavelength value. Laser 0 represents the reference laser wavelength value recorded under the aforementioned reference state. Peak 1 represents the position of the first peak. Peak 0 represents the position of the second peak.

[0020] In some embodiments, the abscissa of the spectrum is corrected based on the current laser wavelength value, including: The spectral abscissa is redefined using the current laser wavelength value; By using multiple spline interpolation algorithms, the spectral data after the x-axis has been redefined is aligned with the pre-stored reference spectral model database with wavenumber as the x-axis.

[0021] According to a third aspect of this application, a gas concentration calibration method is provided, applied to a Fourier transform infrared mixed gas calibration device as described in any embodiment of the first aspect, the gas concentration calibration method comprising: Acquire the current calibration spectrum collected by the Fourier transform infrared mixed gas calibration device; Based on the current calibration spectrum, a first concentration value of at least one component in the calibration gas within the sealed chamber under the current state is obtained through quantitative analysis; Based on the first concentration value and the pre-stored reference concentration value, a correction coefficient for concentration correction is determined; wherein the reference concentration value is a second concentration value calculated and stored for the corresponding component of the calibration gas under reference conditions; The concentration calculation of the gas sample to be tested is corrected using the aforementioned correction coefficient.

[0022] In some embodiments, a correction coefficient k = C0 / C1 for concentration correction is determined based on the first concentration value and a pre-stored reference concentration value. Wherein, C0 is the reference concentration value, and C1 is the first concentration value.

[0023] According to a fourth aspect of this application, a preparation method is provided for preparing a Fourier transform infrared mixed gas calibration device as described in any embodiment of the first aspect, the preparation method comprising: Provides a metal substrate and two window plates; The edges of the window sheet are subjected to surface activation treatment, and a coating structure is formed by depositing a film on the edges of the window sheet. The two window pieces are respectively hermetically welded onto the metal substrate through the coating structure.

[0024] In some embodiments, prior to surface activation treatment of the edges of the window sheet, the preparation method further includes: The welding surface of the metal substrate and the edges of the window piece are cleaned.

[0025] In some embodiments, surface activation treatment is applied to the edges of the window panel, including: The edges of the window are chemically etched to increase its surface roughness.

[0026] In some embodiments, a coating structure is formed by coating the edge of the window sheet, including: Titanium, nickel and gold layers are sequentially deposited at the edge of the activated window. The titanium layer has a thickness of 0.02 μm to 1 μm, the nickel layer has a thickness of 3 μm to 5 μm, and the gold layer has a thickness of 1.3 μm to 5 μm.

[0027] In some embodiments, the two window panes are hermetically welded onto the metal substrate via the coating structure, including: Using indium-based solder and in an inert gas protective environment, the window with the coating structure is welded to the metal substrate. The welding process includes a stepped heating stage and a slow cooling stage. The stepped heating stage includes: heating to 95°C to 105°C at a heating rate of 0.8°C / min to 1.2°C / min and holding for 18 min to 22 min; then heating to 125°C to 135°C and holding for 28 min to 32 min; and then heating to 155°C to 165°C and holding for 8 min to 12 min. The slow cooling stage includes: cooling to 95°C to 105°C at a cooling rate of 0.8°C / min to 1.2°C / min, and then cooling to room temperature at a cooling rate of 2.8°C / min to 3.2°C / min.

[0028] In the Fourier transform infrared mixed gas calibration device of this application embodiment, a metal substrate with a through-hole is used, combined with two windows with coated edges. The coated structures are used to hermetically weld the windows to the metal substrate and cover both ends of the through-hole, thus forming a sealed chamber for containing the calibration gas. This structure, through direct welding and encapsulation of the metal and windows, achieves stable isolation between the calibration gas and the external environment, avoiding changes in the composition or concentration of the calibration gas caused by external temperature, humidity, and contaminant intrusion, providing a long-term stable built-in reference standard for the instrument. Furthermore, the welding seal eliminates the risk of gas leakage and optical path deviation caused by aging or loosening of the sealing ring, significantly improving the physical stability and environmental adaptability of the device. Therefore, this device can provide a constant, reliable, and maintenance-free built-in gas scale for the Fourier transform infrared spectrometer, effectively overcoming the shortcomings of frequent operation and insufficient stability of traditional external standard gas calibration methods, and providing a structural basis for long-term, accurate automatic calibration of the instrument.

[0029] The laser wavelength calibration method of this application obtains the current calibration spectrum of a known calibration gas in a built-in sealed chamber and compares its characteristic absorption peak position with the pre-stored reference peak position to obtain the actual laser wavelength value of the current instrument system. This method utilizes a stably packaged calibration gas as a long-term reliable wavelength reference, enabling direct and accurate quantification of wavelength drift caused by laser aging or changes in ambient temperature. By real-time correction of the spectral abscissa based on this laser wavelength value, the resulting peak position shift is effectively eliminated, ensuring the accuracy of the wavenumber axis upon which qualitative and quantitative spectral identification and analysis depend. This significantly improves the measurement stability and data reliability of the Fourier transform infrared spectrometer during long-term operation.

[0030] The gas concentration calibration method of this application obtains the current spectrum of a calibration gas with known components in a built-in sealed chamber and calculates its current concentration value. This value is then compared with a pre-stored reference concentration value to determine a correction coefficient. This method utilizes a stably stored calibration gas as a long-term, unchanging concentration reference, accurately capturing and quantifying overall concentration response deviations caused by system factors such as instrument optical component attenuation and detector sensitivity changes. By applying this correction coefficient to the concentration calculation results of the subsequent analyte gas, the quantitative analysis capability of the system is directly corrected, effectively compensating for instrument performance drift. This significantly improves the accuracy and reliability of concentration data from long-term online monitoring by a Fourier transform infrared spectrometer without the need for external standard gases.

[0031] The fabrication method of this application involves surface activation treatment of the window edge to form a coated structure, followed by hermetically sealed welding to a metal substrate, creating an integrated sealed chamber. This method, through surface activation and multi-layer metal coating, establishes a robust and compatible transition interface between the infrared optical window and the metal substrate, effectively avoiding interfacial stress and sealing failure caused by differences in material thermal expansion coefficients. The resulting calibration device achieves long-term, stable storage of calibration gas, providing a built-in, maintenance-free, reliable calibration reference for the Fourier transform infrared spectrometer, ensuring the long lifespan and high stability of the calibration device.

[0032] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0035] Figure 1 This is a schematic diagram of the structure of a Fourier transform infrared mixed gas calibration device provided in one embodiment of this application; Figure 2 This is a front view schematic diagram of the Fourier transform infrared mixed gas calibration device provided in one embodiment of this application; Figure 3 It is along Figure 2 Schematic diagram of the cross-sectional structure along line AA; Figure 4 yes Figure 3 Enlarged view of region A in the middle; Figure 5 This is a schematic diagram of the coating structure provided in one embodiment of this application; Figure 6 yes Figure 2 A schematic diagram of the three-dimensional structure after the middle structure is cut along line AA; Figure 7 yes Figure 6 Enlarged view of region B in the middle; Figure 8 This is a schematic diagram of the structure of a Fourier transform infrared mixed gas calibration device provided in another embodiment of this application; Figure 9This is a flowchart of a laser wavelength calibration method provided in one embodiment of this application; Figure 10 This is a flowchart of a gas concentration calibration method provided in one embodiment of this application; Figure 11 This is a flowchart of a preparation method provided in one embodiment of this application.

[0036] Explanation of reference numerals in the attached figures: 100-Metal substrate; 110-Light-transmitting hole; 111-Stepped surface; 120-Sealed chamber; 130-Inflation hole; 131-Connecting section; 132-Sealing section; 200-Window plate; 300-Coated structure; 310-First metal layer; 320-Second metal layer; 330-Third metal layer; 400-Sealing assembly; 410-Sealing plug; 420-Sealant; 500-Base; 510-Guiding structure; 600-Drive mechanism. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0038] Please see Figures 1 to 8 This application provides a Fourier transform infrared (FTIR) mixed gas calibration device. The core function of this device is to provide a long-term stable gas calibration reference for the Fourier transform infrared spectrometer.

[0039] See Figure 1 , Figure 2 , Figure 3 and Figure 4 The core calibration module of this Fourier transform infrared mixed gas calibration device includes a metal substrate 100 and two windows 200. The metal substrate 100 is the core structural component of the device, serving as support and providing a sealed enclosure. A through-hole 110 is machined into the metal substrate 100. This through-hole 110 is the physical channel for the infrared beam, allowing the infrared light emitted by the Fourier transform infrared spectrometer to pass completely through the device. The two windows 200 are optical elements that transmit infrared light, and are fixed to both ends of the through-hole 110. The windows 200 can be made of a material with high transmittance in the infrared band to allow infrared light to pass through efficiently for spectral measurement.

[0040] To improve sealing performance and achieve stable sealing over long periods, each window 200 has a coating structure 300 at its edge. The main function of this coating structure 300 is to facilitate the transition of material properties, transforming the non-metallic surface of the optical window 200 into a weldable metallic surface. The two window 200s are respectively connected to the metal substrate 100 via their edge coating structures 300 through welding to achieve an airtight connection. Here, "airtight connection" means that the sealing level at the connection is sufficient to confine calibration gas within the sealed cavity for an extended period.

[0041] Through the aforementioned connection method, the two windows 200 and the metal substrate 100 together form a completely sealed chamber 120. This sealed chamber 120 is used to encapsulate a calibration gas mixture of specific components and concentrations. These calibration gases are filled during the device manufacturing process and sealed stably over a long period of time, serving as a reference for the periodic calibration of the instrument.

[0042] This structure employs a direct-welded, integrated encapsulation, achieving long-term, stable isolation of the calibration gas from the external environment. This effectively prevents changes in calibration gas composition or concentration drift caused by variations in ambient temperature and humidity, or the infiltration of atmospheric pollutants, reducing instability issues arising from connection leaks. Furthermore, this structure eliminates the need for elastic seals such as O-rings, fundamentally eliminating the risks of gas leakage and minor optical path changes caused by aging, creep, or failure of sealing materials at high and low temperatures. The welded, integrated structure provides the device with stronger resistance to mechanical vibration and impact, as well as a wider operating temperature range, making it suitable for various harsh industrial environments and long-term online monitoring environments.

[0043] In some embodiments, the metal substrate 100 is made of Kovar alloy, and the window 200 is a zinc selenide glass sheet. Kovar alloy is a constant-expansion iron-nickel-cobalt alloy, whose core characteristic is its low coefficient of thermal expansion, which matches that of many hard glass and ceramic materials. In this embodiment, 4J29 alloy can be used, but it can also be replaced with others, such as 29HK, KV-1, etc. Zinc selenide (ZnSe) is a high-performance infrared optical material that exhibits extremely high transmittance in a wide infrared band from 2 micrometers to 20 micrometers, meeting the application requirements of most Fourier transform infrared gas analysis. The coefficient of thermal expansion of zinc selenide material is approximately 7.1 × 10⁻⁶. -6 / ℃, while the coefficient of thermal expansion of Kovar alloy is approximately 5.0 × 10⁻⁶. -6 / ℃ to 5.8×10 -6 / ℃, and the two values ​​are close. Matching the coefficients of thermal expansion can minimize the internal stress caused by thermal expansion and contraction between the metal substrate 100 and the zinc selenide window 200 during the welding process and the temperature changes experienced by the instrument during long-term use.

[0044] Please see Figure 3 and Figure 4 In some embodiments, the coating structure 300 is formed within an annular region at the edge of the window 200. This "annular region" specifically refers to the ring-shaped surface surrounding the optically transparent area of ​​the window 200, reserved for welding to the metal substrate 100. This region serves to achieve mechanical connection and hermetic sealing between the window 200 and the metal substrate 100, providing sufficient and reliable welding surfaces to meet the requirements of welding strength and hermeticity. Furthermore, it is completely located outside the optically transparent area, thereby reducing the obstruction of the effective infrared beam used for spectral measurement by the coating material or the introduction of unnecessary scattering, reflection, or other interference, ensuring the purity of the measurement optical path and the accuracy of the calibration spectrum.

[0045] Specifically, the coating structure 300 is formed on the outer peripheral surface of the edge of the window piece 200 and on the surface extending inward from the edge, i.e., the aforementioned annular region.

[0046] Specifically, the width L of the annular region is less than or equal to 1.5 mm. Controlling the width L within this range minimizes the potential impact of this non-optical functional area on the effective optical path. An excessively wide annular region would unnecessarily reduce the actual light-transmitting area of ​​the window 200, potentially affecting the light spot transmission or edge light quality in extreme cases. Minimizing this size ensures that the infrared beam can completely pass through the central optical quality area of ​​the window 200, avoiding light scattering, reflection, or obstruction that may be caused by edge coatings or welding interfaces, thereby guaranteeing the accuracy and signal-to-noise ratio of the measured spectral signal. Optionally, the width dimension L can be from 0.5mm to 1.5mm, for example, it can be any width value or a range between any two width values ​​from 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, and 1.5mm. By controlling the width dimension L within this range, the coating structure 300 and the solder can be fully spread and form a weld with the necessary mechanical strength and sealing integrity, thereby meeting the stringent requirements of the calibration device for long-term airtightness.

[0047] See Figure 4 and Figure 5 The coating structure 300 includes a first metal layer 310, a second metal layer 320, and a third metal layer 330 sequentially stacked on the edge surface of the window 200, with the chemical reactivity of these three metal layers decreasing sequentially. This "chemical reactivity" refers to the tendency of an element or material to combine with other substances. Materials with higher reactivity are more likely to form stronger chemical bonds with adjacent materials.

[0048] By configuring the coating structure 300 as a multi-layer structure with progressively decreasing chemical activity, a highly reliable seal is achieved between the infrared optical window 200 and the metal substrate 100. This results in a gradient interface with a smooth transition in both physical and chemical properties from the window 200 body to the outermost welding interface.

[0049] Specifically, the first metal layer 310, directly deposited on the surface of the window 200, utilizes its high chemical activity to form strong chemical bonds or physical anchoring with the window 200 material (such as zinc selenide), solving the problem of initial adhesion between the coating and the substrate. The subsequently deposited second metal layer 320, with moderate chemical activity, forms a good bond with the first metal layer 310 and also acts as a stress buffer and diffusion barrier. The outermost third metal layer 330, due to its extremely low chemical activity (i.e., chemical stability and inertness), effectively prevents oxidation during subsequent storage and soldering processes, providing a clean and easily wettable surface for high-quality, high-reliability brazing connections with the metal substrate 100.

[0050] In some embodiments, the first metal layer 310 is a titanium layer, the second metal layer 320 is a nickel layer, and the third metal layer 330 is a gold layer. The window 200 is welded to the metal substrate 100 through the gold layer. Due to its extremely high chemical reactivity, the titanium layer is placed as the innermost layer, directly contacting the substrate of the window 200. It can form a strong chemical bond with the surface of optical materials such as zinc selenide, thus providing crucial initial adhesion and making the entire coating structure 300 difficult to peel off. The nickel layer is located above the titanium layer. It has good ductility and the ability to form good metallurgical bonds with both titanium and gold. One of its core functions is as an effective diffusion barrier layer, preventing the migration of outer gold atoms to the inner layer and the diffusion of inner titanium atoms to the outer layer, thereby maintaining the stability of the interfaces between layers after long-term use and thermal processes. Furthermore, the nickel layer has a moderate coefficient of thermal expansion, which can effectively buffer and absorb thermal stress caused by the difference in the coefficients of thermal expansion between titanium, gold, and the window 200 and the metal substrate 100, improving the structure's resistance to thermal fatigue. The gold layer is placed on the outermost layer, taking advantage of its extremely low chemical reactivity. Gold hardly oxidizes in air, always maintaining an extremely clean and highly active surface energy state. This characteristic allows the brazing filler metal to achieve excellent wetting and spreading during welding, forming a dense, defect-free, and high-strength airtight weld. Therefore, the gold layer directly solves the "weldability" problem when welding to the metal substrate.

[0051] The coating structure 300 uses a combination of titanium, nickel and gold materials. Through their respective chemical and physical properties, it achieves a synergistic relationship from bottom layer adhesion, intermediate layer stress buffering and stabilization to surface layer weldability, thereby ensuring a long-term and reliable gas-tight connection between the window piece 200 and the metal substrate 100.

[0052] In some embodiments, the thickness of the first metal layer 310 is from 0.02 μm to 1 μm, for example, it can be any size value or a range between any two size values ​​selected from 0.02 μm, 0.05 μm, 0.1 μm, 0.12 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.33 μm, 0.4 μm, 0.5 μm, 0.62 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1 μm. Controlling the thickness of the first metal layer 310 within the above range allows it to fully exert its ability to form a high-strength chemical bond with the substrate of the window sheet 200. A thickness less than 0.02 μm may lead to discontinuities in the film layer, affecting the uniformity and reliability of the adhesion. On the other hand, an excessively thick titanium layer (e.g., significantly exceeding 1 μm) is prone to cracking under thermal stress, and is also unnecessary from a cost-effectiveness perspective.

[0053] The thickness of the second metal layer 320 is from 3 μm to 5 μm, for example, it can be any size value or a range between any two sizes from 3 μm, 3.3 μm, 3.7 μm, 4 μm, 4.2 μm, 4.25 μm, 4.3 μm, 4.5 μm, 4.7 μm, 4.9 μm, to 5 μm. Controlling the thickness of the second metal layer 320 within this range can reliably act as a diffusion barrier layer, preventing the interdiffusion of atoms between the upper and lower metal layers and maintaining the long-term stability of the interface; and it can also absorb and buffer thermal stress caused by the mismatch of thermal expansion coefficients of different materials by utilizing its good plasticity and moderate thickness. A thickness of less than 3 μm may not be able to completely block diffusion and has limited stress buffering capacity; while a thickness of more than 5 μm will unnecessarily increase manufacturing costs and interfacial stress.

[0054] The thickness of the third metal layer 330 is from 1.3 μm to 5 μm, for example, it can be any size value or a range between any two sizes, such as 1.3 μm, 1.5 μm, 2 μm, 2.12 μm, 2.25 μm, 3.4 μm, 4.5 μm, 4.7 μm, and 5 μm. Controlling the thickness of the third metal layer 330 within this range ensures complete and continuous coverage of the underlying second metal layer 320 (nickel layer), guaranteeing an oxide-free and clean surface throughout the welding area. A thickness less than 1.3 μm may result in pinholes or uneven coverage, potentially affecting solderability in localized areas due to minute nickel diffusion during subsequent welding or storage. While a thickness exceeding 5 μm can also guarantee performance, the high cost of gold means that excessive thickness will significantly increase material costs without providing a significant performance improvement.

[0055] In some embodiments, the surface roughness of the coated structure 300 is controlled between 0.8 μm and 1.6 μm. For example, it can be any value or a range between any two of 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, and 1.6 μm. Controlling the surface roughness of the coated structure 300 within this range of 0.8 μm to 1.6 μm enables the achievement of a high-strength, high-toughness, and dense ideal welding interface. This ensures that the coated structure 300 itself has sufficient surface area to promote mechanical bonding, while avoiding structural weaknesses introduced by excessive roughness, thus guaranteeing the long-term reliability of the weld seal. When the surface roughness of the coated structure 300 is below 0.8 μm, the surface is too smooth, which will significantly reduce the actual contact area and mechanical engagement between the solder and the gold plating layer during subsequent welding. Conversely, if the surface roughness exceeds 1.6 μm, the excessively rough surface may contain deep holes or gaps that are not completely covered by the metal coating. These defects can become potential channels for gas leakage, directly endangering the airtightness of the sealed chamber 120.

[0056] Please see again Figure 3 and Figure 4 In some embodiments, the light-transmitting aperture 110 is a stepped aperture, with stepped surfaces 111 formed at both ends of its aperture wall. The window piece 200 is welded to this stepped surface 111 via a coating structure 300. The stepped surface 111 provides a precise axial positioning reference for the installation of the window piece 200. During assembly, the window piece 200 can directly abut against the stepped surface 111, which ensures the parallelism between multiple window pieces 200 after installation, as well as the perpendicularity between the window piece 200 and the optical path axis. This maintains optical path collimation, avoids beam deviation or aberrations, and thus ensures the accuracy of subsequent spectral measurement results.

[0057] Furthermore, the stepped surface 111 significantly increases the welding contact area between the coated structure 300 of the window slab 200 and the metal substrate 100. This effectively improves the mechanical strength of the welded joint, making it more resistant to vibration and impact, and significantly enhances the reliability of the seal. It provides structural assurance for the long-term, stable, and high airtightness of the sealed chamber 120.

[0058] See Figure 6 and Figure 7In some embodiments, the metal substrate 100 is further provided with an inflation port 130, which communicates with the sealed chamber 120. The device also includes a sealing plug 410 disposed within the inflation port 130, which achieves an airtight connection with the metal substrate 100. The inflation port 130 serves as a process channel; after the window 200 and the metal substrate 100 are welded together to form the sealed chamber 120, a pre-prepared calibration gas mixture with known components and concentrations is injected into the chamber through this port. After the inflation process is completed, the sealing plug 410 is precisely installed within the inflation port 130 and forms an airtight connection with the hole wall of the metal substrate 100.

[0059] In some embodiments, the inflation port 130 comprises two sections: a connecting section 131 and a sealing section 132. The cross-sectional dimension of the connecting section 131 is smaller than that of the sealing section 132. This allows the inflation port 130 to form an overall stepped or conical channel. The connecting section 131, acting as a gas passage, is directly connected to the sealing chamber 120. Its smaller size helps reduce the cross-sectional area requiring sealing during subsequent sealing processes, thus lowering the sealing difficulty. The sealing section 132 is larger than the connecting section 131, and its main function is to provide sufficient space to accommodate and secure the sealing plug 410. This larger space allows for the use of a larger, more robust sealing plug 410 and provides convenient operating space for implementing the sealing process, contributing to a more robust and reliable sealing structure.

[0060] A sealing plug 410 is positioned within this larger sealing section 132. To ensure absolute sealing reliability, sealant 420 is applied to both ends of the sealing plug 410. The sealing plug 410 and sealant 420 together form the sealing assembly 400, which greatly enhances the redundancy and reliability of the seal. Even if the performance of the sealant 420 at one end slightly decreases due to long-term aging or temperature cycling, the seal at the other end can still effectively maintain the overall airtightness, thereby maximizing the long-term stability of the calibration gas concentration within the sealed chamber 120.

[0061] See Figure 8 In some embodiments, the Fourier transform infrared mixed gas calibration device further includes a base 500 and a drive mechanism 600. The base 500 serves as the mounting base for the entire device and is provided with a guide structure 510. The guide structure 510 can be a mechanical guide element such as a guide rail or a slide, and its core function is to provide constraints for the calibration module composed of the metal substrate 100 and the connected window piece 200, so that it can only move along a preset straight trajectory.

[0062] The drive mechanism 600 is fixedly mounted on the base 500, and its drive end is connected to the metal substrate 100. This mechanism provides power to drive the metal substrate 100 to move precisely in a straight line along the guide structure 510 on the base 500. Optionally, the drive mechanism 600 can be a micro linear motor, a stepper motor with a lead screw, or other components capable of precise position control.

[0063] This allows the sealed chamber 120 containing the built-in calibration gas to switch between two optical path states according to instructions: one is to be precisely moved into the optical path of the Fourier transform infrared spectrometer, allowing the infrared beam to completely pass through the chamber, at which point the instrument performs calibration measurements; the other is to be moved out of the optical path, allowing the infrared beam to directly irradiate the sample to be tested, at which point the instrument performs normal gas sample analysis. This enables the instrument to automatically and efficiently complete periodic calibration and continuous sample measurements, greatly improving the instrument's automation level and the reliability of long-term online monitoring.

[0064] Corresponding to the aforementioned Fourier transform infrared mixed gas calibration device, this application also provides a calibration method applied to the Fourier transform infrared mixed gas calibration device. This calibration method includes: a laser wavelength calibration method and a gas concentration calibration method.

[0065] The core of the laser wavelength calibration method is to use a calibration gas with known composition and stable properties sealed in the device as a long-term reliable wavelength reference to correct the measurement error caused by the laser wavelength drift in the Fourier transform infrared spectrometer in real time.

[0066] Specifically, see Figure 9 In some embodiments, the laser wavelength calibration method includes: The calibration spectrum under the current state is acquired through the calibration device. Since the composition and concentration of the calibration gas within the sealed chamber 120 are constant, it possesses fixed and known characteristic absorption peaks in the infrared band. Therefore, these characteristic absorption peaks can be accurately identified and located from the current calibration spectrum, yielding the position of the first peak.

[0067] The currently measured first peak position is compared with the pre-stored reference peak position. This reference peak position is the second peak position of the corresponding characteristic absorption peak measured on the same calibration gas under the reference state, either at the instrument's factory or during the last fine calibration. Since the laser wavelength under the reference state is known and accurate, any systematic shift in the current peak position can be attributed to a laser wavelength drift. The actual current laser wavelength value can then be calculated based on this shift using a specific algorithm or formula.

[0068] Using the calculated current laser wavelength value, the abscissa (wavenumber or wavelength coordinate) of all subsequent measured spectral data is systematically corrected. This ensures that the abscissa reference of subsequent spectra remains consistent with the coordinate reference under the reference state.

[0069] This method, through a built-in, stable gas reference, transforms the internal wavelength drift of the laser, which is difficult to measure directly, into a precisely measurable spectral peak shift, and achieves real-time, online correction of the spectral abscissa. This effectively compensates for spectral drift caused by laser aging or changes in ambient temperature, fundamentally ensuring the long-term accuracy, stability, and reliability of the Fourier transform infrared spectrometer in qualitative and quantitative analysis of substances, and achieving autonomous calibration without the need for external wavelength standards.

[0070] In some embodiments, the current laser wavelength value is determined based on the first peak position and a pre-stored reference peak position using the following formula:

[0071] Laser1 is the current laser wavelength value; Laser 0 represents the reference laser wavelength value recorded under the reference state, which is pre-calibrated and stored under the reference state; Peak 1 represents the position of the first peak, which is the position of the characteristic absorption peak actually calculated from the currently acquired calibration spectrum; Peak 0 represents the position of the second peak, which is the reference position of the corresponding characteristic absorption peak measured in advance under the reference conditions.

[0072] This allows for high-precision wavelength calibration through internal comparison of spectral data, effectively ensuring the consistency of the calibration process and the accuracy of the results.

[0073] In some embodiments, the abscissa of the spectrum is corrected based on the current laser wavelength value, including: The abscissa of the spectrum is redefined using the current laser wavelength value. This involves recalculating and calibrating the abscissa of the spectrum using the previously calculated current laser wavelength value. This corrects the scaling distortion of the entire wavenumber axis caused by laser wavelength drift, establishing a correct coordinate reference for subsequent data alignment.

[0074] Then, through multiple spline interpolation algorithms, the spectral data with the recalibrated abscissa is aligned with a pre-stored reference spectral model database using wavenumber as the abscissa. Specifically, a cubic spline interpolation algorithm is used to align the spectral data of the sample to be tested, after recalibration of the abscissa, with the pre-stored reference spectral model database. This database refers to a collection of standard spectral data containing different substances at different concentrations, established at the instrument's factory or under standard conditions, whose abscissa wavenumber values ​​are accurate and reliable.

[0075] This ensures that the spectrum of the sample under test can be accurately compared with the spectrum in the benchmark model library at the same wavenumber scale during subsequent qualitative identification and quantitative analysis, thus guaranteeing the accuracy of the analysis results.

[0076] Correspondingly, the core purpose of the gas concentration calibration method is to quantify and correct the concentration response drift of the entire optical and detection system of the instrument caused by long-term operation through the built-in calibration gas reference, thereby ensuring the long-term accuracy of quantitative gas concentration analysis.

[0077] See Figure 10 In some embodiments, the gas concentration calibration method includes: The calibration spectrum under the current condition is acquired through the calibration device. Since the concentrations of each component of the calibration gas within the sealed chamber 120 are known and constant, theoretically, the calculated concentration measured by the instrument at any time should be consistent with this known concentration.

[0078] Based on the currently acquired calibration spectrum, the instrument uses a pre-stored quantitative analysis algorithm to calculate the first concentration value of at least one calibration gas component within the sealed chamber 120 under the current instrument conditions. This calculated concentration value reflects the instrument's "response value" to the gas of known concentration at the current moment.

[0079] The calculated first concentration value is compared with a pre-stored reference concentration value to determine a coefficient for concentration correction. This reference concentration value is a second concentration value calculated and saved for the same calibration gas component under reference conditions, either at the instrument's factory settings or during the last fine calibration. Under reference conditions, the instrument's response is accurate, therefore this reference concentration value should be equal to or very close to the gas's true known concentration.

[0080] By comparing the current calculated concentration with the reference concentration, the extent to which the overall response of the instrument system (including the light source, detector, optical components, etc.) has drifted relative to the reference state can be quantified. The correction coefficient calculated based on this can directly characterize the proportional relationship of this drift.

[0081] When calculating the concentration of the gas sample, this correction factor is applied to the calculation results. This is equivalent to "pulling" the instrument's current response characteristics back to the baseline state, thereby compensating for the overall drift of the system.

[0082] This method utilizes a stable, sealed gas reference to achieve online monitoring and automatic correction of concentration response drift across the entire instrument system. This solves the problem of long-term measurement deviations caused by factors such as optical window contamination, light source attenuation, and detector sensitivity variations. It enables the instrument to maintain accurate concentration measurements without the need for external standard gases, significantly improving the reliability and data quality of Fourier transform infrared gas analyzers in long-term online monitoring applications.

[0083] In some embodiments, a correction coefficient k = C0 / C1 is determined for concentration correction based on a first concentration value and a pre-stored reference concentration value; where C0 is the reference concentration value and C1 is the first concentration value. The degree of system drift is quantified by calculation, and a uniform scaling factor is used to systematically correct the measurement results of all subsequent samples. This method requires no complex model adjustments or parameter fitting, is simple to operate, computationally stable, and can effectively compensate for slow, systematic concentration measurement deviations caused by long-term operation or environmental changes in the instrument system, thereby reliably maintaining the accuracy of quantitative analysis results.

[0084] Corresponding to the above-mentioned Fourier transform infrared mixed gas calibration device, this application embodiment also provides a preparation method, referring to... Figure 11 The preparation method includes: A metal substrate 100 and two windows 200 are provided. This constitutes the preparation of the basic materials. The metal substrate 100 is pre-machined with a through-hole 110 and other related structures, while the windows 200 are made of optical materials that meet the requirements for infrared transmission.

[0085] The edges of the window 200 undergo surface activation treatment, and a coating is deposited in the activated area to form a coating structure 300. This step ensures a high-adhesion, high-reliability bond between different materials. Surface activation treatment, such as chemical etching with hydrofluoric acid solution, aims to increase the surface roughness of the edge area of ​​the window 200 and improve its surface chemical state, providing stronger mechanical anchoring points and a chemical bonding basis for subsequent metal plating. The subsequent coating process forms a metal transition layer on this activated surface, and this coating structure 300 forms the interface for subsequent hermetic welding.

[0086] Two windows 200 are hermetically welded to the metal substrate 100 via the formed coating structure 300. This step achieves stable encapsulation through the welding process. A dense, strong weld that meets long-term hermeticity requirements is formed between the coating structure 300 and the metal substrate 100, thereby ultimately forming a sealed chamber 120 for containing calibration gas.

[0087] The calibration device prepared by this method has excellent airtightness, mechanical stability and environmental adaptability, and can provide a long-life, maintenance-free built-in calibration reference for Fourier transform infrared spectrometers.

[0088] In some embodiments, before surface activation treatment of the edge of the window piece 200, the preparation method further includes cleaning the welding surface of the metal substrate 100 and the edge of the window piece 200. This cleaning step can remove various contaminants that may have adhered to the welding surface of the metal substrate 100 and the edge of the window piece 200 during processing, handling and storage, including but not limited to grease, dust, fingerprints, fine particulate matter and certain organic or inorganic residues.

[0089] By employing appropriate cleaning agents and cleaning processes (such as ultrasonic cleaning combined with solvents such as acetone, ethanol, and deionized water), a highly clean and active surface state is provided for subsequent surface activation and welding processes.

[0090] In some embodiments, the edges of the window 200 are subjected to surface activation treatment, including chemical etching of the edges of the window 200 to increase its surface roughness. Chemical etching is a surface treatment process that alters the morphology and chemical state of a material surface through a selective reaction of chemical reagents with the surface. In this preparation method, a specific etching solution (such as a hydrofluoric acid-based solution) is used to treat the edges of the zinc selenide infrared optical window 200. This improves the stability of the entire multilayer coating structure 300 and the long-term reliability of the final welded seal.

[0091] In some embodiments, a coating structure 300 is formed by depositing a coating on the edge of the window 200, including: sequentially depositing a titanium layer, a nickel layer and a gold layer on the edge of the activated window 200; wherein the thickness of the titanium layer is 0.02 μm to 1 μm, the thickness of the nickel layer is 3 μm to 5 μm, and the thickness of the gold layer is 1.3 μm to 5 μm.

[0092] In some embodiments, the two window pieces 200 are hermetically welded to the metal substrate 100 via a coating structure 300, including: Using indium-based brazing filler metal and under an inert gas protective environment, the window 200 with the coated structure 300 is welded to the metal substrate 100 using low-temperature welding. Indium-based brazing filler metal is a low-melting-point metal welding material; the lower welding temperature avoids thermal damage to the zinc selenide window 200 caused by high temperatures, preventing degradation of its optical properties, and also protects the already formed precision coated structure 300. The inert gas protective environment (such as the introduction of high-purity nitrogen) effectively prevents oxidation of the weld interface during heating, ensuring a high-quality metallurgical bond.

[0093] The welding process includes a stepped heating stage and a slow cooling stage: The stepped heating stage includes: heating to 95℃ to 105℃ at a rate of 0.8℃ / min to 1.2℃ / min and holding for 18min to 22min; then heating to 125℃ to 135℃ and holding for 28min to 32min; and then heating to 155℃ to 165℃ and holding for 8min to 12min; achieving a stable and uniform temperature rise. This allows the metal substrate 100, the coating structure 300, and the window 200 within the device to be heated synchronously and uniformly, ensuring that processes such as solvent evaporation, solder melting, and flow proceed smoothly. This minimizes instantaneous thermal stress caused by thermal shock and differences in the coefficients of thermal expansion between different materials, thereby preventing cracking of the brittle window 200 or damage to the coating structure 300.

[0094] The slow cooling stage includes cooling to 95°C to 105°C at a rate of 0.8°C / min to 1.2°C / min. This process allows the weld to fully relax in its high-temperature plastic state, further releasing residual welding stress. Then, the weld is cooled to room temperature at a rate of 2.8°C / min to 3.2°C / min. This improves production efficiency without introducing new thermal stress.

[0095] In some embodiments, an airtightness test is performed after welding to ensure the effectiveness of the welding.

[0096] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0097] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0098] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0099] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A Fourier infrared mixed gas calibration apparatus, characterized by, The application relates to a Fourier infrared mixed gas calibration device. The metal base (100) is made of Kovar alloy, and the window sheet (200) is made of zinc selenide glass sheet. The film coating structure (300) is formed in an annular area of the edge of the window sheet (200) for welding with the metal base (100).

2. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, The width dimension L of the annular area is less than or equal to 1.5 mm.

3. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, The film coating structure (300) comprises a first metal layer (310), a second metal layer (320) and a third metal layer (330) which are sequentially stacked on the edge surface of the window sheet (200), and the chemical activity of the first metal layer (310), the second metal layer (320) and the third metal layer (330) is sequentially reduced.

4. The Fourier infrared mixed gas calibration apparatus of claim 3, wherein, The first metal layer (310) is made of titanium, the second metal layer (320) is made of nickel, and the third metal layer (330) is made of gold, and the window sheet (200) is welded with the metal base (100) through the gold layer.

5. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, The thickness of the first metal layer (310) is 0.02-1 mu m, the thickness of the second metal layer (320) is 3-5 mu m, and the thickness of the third metal layer (330) is 1.3-5 mu m.

6. The Fourier infrared mixed gas calibration apparatus of claim 5, wherein, The surface roughness of the film coating structure (300) is 0.8-1.6 mu m.

7. The Fourier infrared mixed gas calibration apparatus according to claim 5 or 6, characterized by The light transmission hole (110) is a stepped hole, and a stepped surface (111) is formed at both ends of the hole wall of the light transmission hole (110), and the window sheet (200) is welded on the stepped surface (111) through the film coating structure (300).

8. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, The metal base (100) is further provided with a gas filling hole (130) which is communicated with the sealed cavity (120).

9. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, The Fourier infrared mixed gas calibration device further comprises a sealing plug (410) which is arranged in the gas filling hole (130) and is airtightly connected with the metal base (100).

10. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, The gas filling hole (130) comprises a communication section (131) and a plugging section (132), the size of the communication section (131) is smaller than that of the plugging section (132), and the communication section (131) is communicated between the sealed cavity (120) and the plugging section (132). The sealing plug (410) is arranged in the plugging section (132), and both ends of the sealing plug (410) are provided with sealing glue (420).

11. The Fourier infrared mixed gas calibration apparatus of claim 10, wherein, The Fourier infrared mixed gas calibration device further comprises: A base (500) provided with a guide structure (510).

12. The Fourier infrared mixed gas calibration apparatus of claim 1, wherein, ​ ​ A driving mechanism (600) is mounted on the base (500) and has a driving end connected to the metal base (100) for driving the metal base (100) to move along the guide structure (510).

13. A method of laser wavelength calibration, characterized by, The laser wavelength calibration method is applied to the Fourier infrared mixed gas calibration device as claimed in any one of claims 1 to 12, and comprises the following steps: Obtaining a current calibration spectrum collected by the Fourier infrared mixed gas calibration device; Based on the current calibration spectrum, determining a first peak position of one or more characteristic absorption peaks of the calibration gas in the sealed chamber (120) in the current state; Based on the first peak position and a pre-stored reference peak position, determining a current laser wavelength value; wherein the reference peak position is a second peak position of a corresponding characteristic absorption peak of the calibration gas measured in a reference state; Based on the current laser wavelength value, correcting the abscissa of the spectrum.

14. The laser wavelength calibration method of claim 13, wherein, Based on the first peak position and a pre-stored reference peak position, the current laser wavelength value is determined by the following formula: wherein Laser1 is the current laser wavelength value, Laser 0 is a reference laser wavelength value recorded in the reference state, Peak 1 is the first peak position, Peak 0 is the second peak position.

15. The laser wavelength calibration method according to claim 13 or 14, characterized in that, Based on the current laser wavelength value, the abscissa of the spectrum is corrected, which comprises the following steps: Redetermining the abscissa of the spectrum by using the current laser wavelength value; Aligning the re-determined abscissa of the spectrum data with a pre-stored reference spectrum model database with wave number as the abscissa in the abscissa by a multiple spline interpolation algorithm.

16. A gas concentration calibration method, characterized by, The gas concentration calibration method is applied to the Fourier infrared mixed gas calibration device as claimed in any one of claims 1 to 12, and comprises the following steps: Obtaining a current calibration spectrum collected by the Fourier infrared mixed gas calibration device; Based on the current calibration spectrum, quantitatively analyzing to obtain a first concentration value of at least one component of the calibration gas in the sealed chamber (120) in the current state; Based on the first concentration value and a pre-stored reference concentration value, determining a correction coefficient for concentration correction; wherein the reference concentration value is a second concentration value of a corresponding component of the calibration gas calculated and saved in a reference state; Using the correction coefficient to correct the concentration calculation of the to-be-tested gas sample.

17. The gas concentration calibration method of claim 16, wherein, Based on the first concentration value and a pre-stored reference concentration value, the correction coefficient k=C0 / C1 for concentration correction is determined. Wherein, C0 is the reference concentration value, and C1 is the first concentration value.

18. A method of manufacture, characterized by, The preparation method for preparing the Fourier infrared mixed gas calibration device as claimed in any one of claims 1 to 12 comprises the following steps: Providing a metal base (100) and two window sheets (200); Performing surface activation treatment on the edges of the window sheets (200) and forming a plated film structure (300) by plating films on the edges of the window sheets (200); Aerostatically welding the two window sheets (200) on the metal base (100) through the plated film structures (300) respectively.

19. The method of claim 18, wherein, Before performing the surface activation treatment on the edges of the window sheets (200), the preparation method further comprises the following steps: Cleaning the welding surface of the metal base (100) and the edges of the window sheets (200).

20. The method of claim 18, wherein, Surface activation treatment is performed on the edge of the window sheet (200), including: Chemical etching is performed on the edge of the window sheet (200) to increase the surface roughness thereof.

21. The method of claim 18, wherein, A film coating structure (300) is formed on the edge of the window sheet (200) by film coating, including: A titanium layer, a nickel layer and a gold layer are sequentially deposited on the edge of the activated window sheet (200); wherein the thickness of the titanium layer is 0.02-1 μm, the thickness of the nickel layer is 3-5 μm, and the thickness of the gold layer is 1.3-5 μm.

22. The preparation method according to claim 18, characterized in that, Two window sheets (200) are respectively hermetically welded to the metal base (100) through the film coating structure (300), including: Inert gas protection environment is adopted, and the window sheet (200) with the film coating structure (300) is welded to the metal base (100) by using indium-based solder, and the welding process includes a stepwise heating stage and a slow cooling stage; the stepwise heating stage includes: heating at a heating rate of 0.8-1.2 ℃ / min to 95-105 ℃ and maintaining for 18-22 min; then continuously heating to 125-135 ℃ and maintaining for 28-32 min; and then continuously heating to 155-165 ℃ and maintaining for 8-12 min; the slow cooling stage includes: cooling at a cooling rate of 0.8-1.2 ℃ / min to 95-105 ℃, and then cooling at a cooling rate of 2.8-3.2 ℃ / min to room temperature.

Images