Concha margaritifera quality nondestructive evaluation method based on porosity of three-dimensional structure

Abstract

The invention discloses a mother-of-pearl quality nondestructive evaluation method based on porosity of a three-dimensional structure, and relates to the technical field of mother-of-pearl nondestructive microscopic identification, the method comprises the following steps: respectively calcining mother-of-pearl raw products at a plurality of calcining temperatures by adopting an open calcining method to obtain a plurality of processed products with different processing degrees; respectively carrying out microscopic CT scanning on the mother-of-pearl raw product and each processed product to obtain a plurality of projection drawings; according to the plurality of projection images, performing three-dimensional image reconstruction by adopting a phase recovery algorithm and an iterative reconstruction algorithm to generate three-dimensional data; according to the three-dimensional data, carrying out pore segmentation by adopting an image segmentation algorithm, and calculating to obtain the porosity of the mother-of-pearl raw product and each processed product; and determining the quality grades of the mother-of-pearl raw product and each processed product according to the porosity of the mother-of-pearl raw product and each processed product in combination with the relationship among the porosity, the calcining temperature and the sample quality. According to the invention, nondestructive evaluation of the mother-of-pearl quality can be realized, and the accuracy of mother-of-pearl quality evaluation is improved.

Description

Technical Field

[0001] The present application relates to the technical field of non-destructive microscopic identification of traditional Chinese medicine mother-of-pearl, and in particular to a non-destructive evaluation method for mother-of-pearl quality based on three-dimensional structural porosity. Background Art

[0002] Mother of pearl is the main representative of marine Chinese medicine, and is often forged by the bright calcination method to obtain processed products. Traditional methods for identifying the quality of mother of pearl include property identification, microscopic identification, and physical and chemical identification. Among them, the property identification method observes its round or irregular flaky morphology and pearl-like luster. Although the operation is simple and intuitive, it is easily affected by the integrity of the sample, resulting in inaccurate identification results. The microscopic identification method uses a polarizing microscope to observe the layered arrangement structure and the overlapping characteristics of the prismatic layers. Although it can distinguish counterfeits, it requires professional equipment and technical support, otherwise it is difficult to guarantee the accuracy of the identification results. The physical and chemical identification method uses methods such as dilute hydrochloric acid reaction (bubble generation), burning experiment (calcium carbonate decomposition) and ultraviolet fluorescence (light blue and white). Although it has strong specificity and rapid identification, some methods are destructive and rely on precision instruments, making it difficult to guarantee the accuracy of the identification results.

[0003] In summary, how to provide a more accurate non-destructive evaluation method for mother-of-pearl quality and improve the accuracy of mother-of-pearl quality evaluation has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0004] The purpose of this application is to provide a method for non-destructive evaluation of mother-of-pearl quality based on three-dimensional structural porosity, which can realize non-destructive evaluation of mother-of-pearl quality and improve the accuracy of mother-of-pearl quality evaluation.

[0005] To achieve the above objectives, this application provides the following solutions.

[0006] A nondestructive evaluation method for mother-of-pearl quality based on three-dimensional structural porosity, the nondestructive evaluation method for mother-of-pearl quality based on three-dimensional structural porosity specifically comprises the following steps.

[0007] The raw mother-of-pearl is calcined at various calcination temperatures using the open calcination method to obtain multiple processed products with different degrees of processing.

[0008] Micro-CT scanning was performed on the raw mother-of-pearl product and each of the processed products to obtain several projection images.

[0009] According to the plurality of projection images, a phase recovery algorithm and an iterative reconstruction algorithm are used to perform three-dimensional image reconstruction to generate three-dimensional data; the three-dimensional data includes a phase contrast micro-CT three-dimensional reconstructed image and a corresponding three-dimensional voxel matrix.

[0010] Based on the three-dimensional data, pore segmentation is performed using an image segmentation algorithm, and the porosity of the raw nacre and each of the processed products is calculated.

[0011] Based on the porosity of the raw nacre and each of the processed products, and in combination with the relationship among porosity, calcination temperature, and sample mass, the quality grades of the raw nacre and each of the processed products are determined.

[0012] Optionally, micro-CT scans are respectively performed on the raw nacre and each of the processed products to obtain a number of projection images, which specifically include the following steps.

[0013] According to the brightness change of the X-ray when the X-ray penetrates the raw nacre and each of the processed products, the micro-CT scan parameters of the micro-CT system are determined.

[0014] Based on the micro-CT scan parameters, using the micro-CT system, micro-CT scans are respectively performed on the raw nacre and each of the processed products to obtain the projection images of the raw nacre and each of the processed products.

[0015] Optionally, the micro-CT system includes an X-ray source for emitting X-rays, and a filter, a monochromator, a specimen stage, and an X-ray detector sequentially arranged along the direction of the X-ray.

[0016] The filter is used to filter the X-ray to remove stray rays.

[0017] The monochromator is used to adjust the energy of the X-ray.

[0018] The specimen stage is used to fix the raw nacre and each of the processed products.

[0019] The X-ray detector is used to collect the projection images of the raw nacre and each of the processed products.

[0020] Optionally, based on the number of the projection images, three-dimensional image reconstruction is performed using a phase retrieval algorithm and an iterative reconstruction algorithm to generate three-dimensional data, which specifically includes the following steps.

[0021] Based on the number of the projection images, the refractive index distribution of the raw nacre and each of the processed products is reconstructed using a phase retrieval algorithm.

[0022] Based on the refractive index distribution of the raw nacre and each of the processed products, three-dimensional CT reconstruction is performed using an iterative reconstruction algorithm to generate the three-dimensional data of the raw nacre and each of the processed products.

[0023] Optionally, before the step of reconstructing the refractive index distributions of the raw nacre and each of the processed products by using a phase retrieval algorithm according to a plurality of the projection images, the non-destructive evaluation method for the quality of nacre based on three-dimensional structural porosity further includes the following steps.

[0024] Geometric correction and noise filtering are respectively performed on each of the projection images to obtain preprocessed projection images; the preprocessed projection images are used as the projection images to reconstruct the refractive index distributions of the raw nacre and each of the processed products by using a phase retrieval algorithm.

[0025] Optionally, the iterative reconstruction algorithm is the FDK algorithm.

[0026] Optionally, according to the three-dimensional data, pore segmentation is performed by using an image segmentation algorithm, and the porosities of the raw nacre and each of the processed products are calculated, which specifically includes the following steps.

[0027] According to the three-dimensional data, an image segmentation algorithm is used to extract a pore-matrix binary three-dimensional structure model.

[0028] Based on the pore-matrix binary three-dimensional structure model, the pore volume and the total sample volume of the raw nacre and each of the processed products are determined.

[0029] According to the pore volume and the total sample volume of the raw nacre and each of the processed products, the porosities of the raw nacre and each of the processed products are calculated.

[0030] Optionally, the image segmentation algorithm is the Otsu algorithm or an image segmentation algorithm based on a U-Net deep learning model.

[0031] Optionally, the porosities of the raw nacre and each of the processed products are calculated by using the following formula: ε = V1 / V2×100%; where ε is the porosity, V1 is the pore volume, and V2 is the total sample volume.

[0032] Optionally, the quality grades include high grade, medium grade, and low grade.

[0033] The value range of the porosity corresponding to the high grade is: ε > 40%.

[0034] The value range of the calcination temperature corresponding to the high grade is: T > 800°C.

[0035] The value range of the porosity corresponding to the medium grade is: 5% ≤ ε ≤ 40%.

[0036] The value range of the calcination temperature corresponding to the medium grade is: 400°C ≤ T ≤ 800°C.

[0037] The value range of the porosity corresponding to the low grade is: ε < 5%.

[0038] The value range of the calcination temperature corresponding to the low grade is: T < 400 °C.

[0039] Where ε is the porosity and T is the calcination temperature.

[0040] According to the specific embodiments provided by the present application, the present application has the following technical effects: The present application provides a non-destructive evaluation method for the quality of nacre based on the porosity of the three-dimensional structure. By using micro-CT scanning technology, micro-CT scanning is performed on the raw nacre and each processed product to obtain projection images, and then three-dimensional image reconstruction is carried out by using the phase recovery algorithm and the iterative reconstruction algorithm to obtain the three-dimensional data of the raw nacre and different processed products without damage. Then, pore segmentation is performed by using the image segmentation algorithm, and the porosity of the raw nacre and each processed product is calculated. Combining the relationship between porosity, calcination temperature and sample quality, the quality grades of the raw nacre and each processed product can be determined without damage. The present application combines micro-CT scanning technology, three-dimensional image reconstruction technology, pore segmentation technology and porosity quantitative evaluation technology, and integrates various algorithms such as the phase recovery algorithm, the iterative reconstruction algorithm and the image segmentation algorithm to realize the quantitative evaluation of the quality of nacre based on the porosity of the three-dimensional microstructure of the raw nacre and the processed products, improve the accuracy of nacre quality evaluation, without damaging samples such as the raw nacre and the processed products, nor using a polarized light microscope to observe the layered arrangement structure and the overlapping characteristics of the prismatic layer, and not relying on precision instruments for physical and chemical identification, realizing efficient, rapid and non-destructive nacre quality evaluation, and ensuring the accuracy of nacre quality evaluation. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0042] Figure 1 It is a schematic flow chart of a non-destructive evaluation method for the quality of nacre based on the porosity of the three-dimensional structure provided by an embodiment of the present application.

[0043] Figure 2 It is a schematic structural diagram of an X-ray micro-CT experimental device used for the non-destructive evaluation method for the quality of nacre based on the porosity of the three-dimensional structure provided by an embodiment of the present application.

[0044] Figure 3Schematic diagram of the three-dimensional structure of raw nacre provided by an embodiment of the present application.

[0045] Figure 4 Schematic diagram of the three-dimensional structure of raw nacre provided by an embodiment of the present application after being processed at 400 °C for 1 h.

[0046] Figure 5 Schematic diagram of the three-dimensional structure of raw nacre provided by an embodiment of the present application after being processed at 600 °C for 1 h.

[0047] Figure 6 Schematic diagram of the three-dimensional structure of raw nacre provided by an embodiment of the present application after being processed at 800 °C for 1 h.

[0048] Reference numerals: 1 - X-ray source; 2 - insert; 3 - filter; 4 - monochromator; 5 - specimen stage; 6 - X-ray detector. Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0050] In view of the limitations of traditional quality identification methods for nacre, modern analysis techniques have achieved breakthroughs through high-precision, non-destructive, and multi-dimensional detection. For example, scanning electron microscopy (SEM) can magnify to the nanoscale to observe the layered structure and overlapping characteristics of the prismatic layer of nacre, with a resolution far exceeding that of traditional microscopic identification, and can intuitively distinguish natural and artificial imitations; X-ray diffraction (XRD) determines the calcium carbonate crystal form by analyzing the ratio of aragonite to calcite, accurately identifying the mineral composition of nacre and avoiding the damage to samples by traditional physical and chemical methods; Fourier transform infrared spectroscopy (FTIR) combines the organic matrix absorption peak at 3440 cm -1 and the CO3 absorption peak at 873 cm -1 2- ​Characteristic peaks such as vibration peaks are used to achieve joint detection of organic and inorganic components, with high sensitivity and no need for pretreatment; inductively coupled plasma mass spectrometry (ICP-MS) can quantify trace elements such as Sr (strontium) and Mg (magnesium), and combined with statistical models to trace the origin, solving the traceability problem that cannot be achieved by traditional methods; Raman spectroscopy can quickly and nondestructively identify the authenticity of nacre through molecular vibration information, which is suitable for on-site detection; HPLC (high performance liquid chromatography) fingerprint maps can quickly analyze the authenticity and quality of medicinal materials through methods such as common peaks and similarity evaluation, comprehensively reflecting the types and contents of chemical components in medicinal materials, and have been widely used in the quality control of Chinese medicinal materials. These modern technologies make up for the deficiencies of traditional methods in terms of resolution, specificity and nondestructive detection, significantly improving the identification efficiency and accuracy, but the equipment cost is relatively high and professional personnel are required for operation.

[0051] Judging from the existing quality standards and relevant research reports of nacre, at present, most of them use the calcium carbonate content as an index for quality control. The high or low content is difficult to reflect the intrinsic pharmacological activity, and it lacks specificity and exclusivity, and cannot fully reflect the characteristics of the decoction pieces and the influence of the processing technology on the quality. At the same time, it has little reference significance for market supervision and it is difficult to fundamentally control the intrinsic quality of medicinal materials. In addition, the mechanism of processing nacre by the calcination method is not clear, the processing methods vary greatly, and the quality standards are not unified, resulting in large differences in the quality of nacre decoction pieces, seriously affecting the safety and effectiveness of clinical medication. In view of the weak research on the effective substance basis and unclear action mechanism of nacre, in order to ensure the quality and reasonable development and utilization of marine Chinese medicinal materials such as nacre, it is very crucial to establish a simple and effective quantitative evaluation method.

[0052] The development of Microscopic Computed Tomography (Micro-CT) technology is rapid. The CT (Computed Tomography) scanner penetrates the object from multiple angles with X-rays and reconstructs tomographic images by computer to achieve three-dimensional nondestructive detection. Its core principle is to use the absorption difference of tissues to X-rays to generate high-resolution cross-sectional images, which has now been widely used in disease diagnosis, industrial flaw detection and cultural relic analysis. As a refined extension of CT technology, Micro-CT uses a microfocus X-ray source (focal spot size <5μm) and a high-resolution flat panel detector (pixel size 10-50μm) to improve the spatial resolution to the sub-micron level (0.5-50μm), which is 2-3 orders of magnitude higher than traditional CT. Its core principle is to obtain thousands of projection images by rotating the sample 360°, and use the filtered back projection algorithm to reconstruct three-dimensional volume data to achieve non-destructive "virtual section" observation, and has gradually been popularized in the fields of biomedicine, engineering physics, etc. in recent years.

[0053] In the field of traditional Chinese medicine quality control, micro-CT shows advantages: it can non-destructively analyze the fine internal structure of medicinal materials, such as the layered aragonite structure of nacre and the coelom structure of Cordyceps sinensis larvae. At the same time, it can accurately identify wormholes, mildew hyphal networks and adulterated substances. Combining energy spectrum technology (such as dual-energy CT) can distinguish chemical composition differences, such as differentiating the calcium-phosphorus ratio differences between collagen from cattle hide and donkey hide in Ejiao. In addition, combined with artificial intelligence algorithms, a digital evaluation system for key parameters such as the porosity and mineralization degree of medicinal materials can be established. Compared with traditional microscopic identification (destructive sectioning, limited field of view) and HPLC (only chemical composition analysis), micro-CT can simultaneously achieve three-dimensional quantitative analysis of morphology-composition-structure on the premise of maintaining the integrity of the medicinal materials, providing an intelligent solution for the standardization and authenticity identification of traditional Chinese medicine.

[0054] In summary, there is an urgent need for a more accurate non-destructive evaluation method for the quality of nacre. Taking porosity as a quantitative index to measure the processing degree and quality grade of nacre, in order to form a quality control mode different from the previous one based on the content limit of chemical index components, providing new ideas and references for the quality control research of marine mineral traditional Chinese medicine.

[0055] To make the above objects, features and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] As Figure 1 shown, this embodiment proposes a non-destructive evaluation method for the quality of nacre based on three-dimensional structure porosity. The non-destructive evaluation method for the quality of nacre based on three-dimensional structure porosity specifically includes the following steps.

[0057] Step S1: Calcinate the raw nacre at various calcination temperatures using the open calcination method to obtain multiple processed products with different processing degrees.

[0058] The raw nacre refers to the original material for processing traditional Chinese medicine nacre. Its dense structure and high calcium carbonate content provide the basis for subsequent calcination processes. The raw nacre is uncalcined, and by subjecting the raw nacre to high-temperature calcination, the corresponding processed products of the raw nacre can be obtained.

[0059] The open calcination method refers to a calcination method without isolating air, which is applicable to relatively easily calcined mineral and animal shell and fossil drugs. The open calcination method decomposes CaCO3 (calcium carbonate) in the raw nacre through high-temperature oxidation to generate a porous CaO (calcium oxide) structure, which is a key step to improve its medicinal efficacy and quality.

[0060] In this embodiment, the raw nacre samples are calcined separately at various calcination temperatures (such as 400 °C, 600 °C, 800 °C) by the open calcination method, and the processed products with different processing degrees can be obtained. The raw nacre samples and the processed products with different processing degrees are used as the test samples simultaneously.

[0061] Step S2: Micro-CT scans are respectively performed on the raw nacre samples and each of the processed products to obtain a number of projection images.

[0062] In this embodiment, in step S2, micro-CT scans are respectively performed on the raw nacre samples and each of the processed products to obtain a number of projection images, which specifically includes the following steps.

[0063] Step S21: According to the brightness change of the X-ray when the X-ray penetrates the raw nacre samples and each of the processed products, the micro-CT scan parameters of the micro-CT system are determined.

[0064] Step S22: Based on the micro-CT scan parameters, using the micro-CT system, micro-CT scans are respectively performed on the raw nacre samples and each of the processed products to obtain the projection images of the raw nacre samples and each of the processed products.

[0065] In this embodiment, a micro-CT system is used for micro-CT scanning. The micro-CT system includes an X-ray source 1 for emitting X-rays, and a filter 3, a monochromator 4, a specimen stage 5, and an X-ray detector 6 arranged in sequence along the direction of the X-ray, as Figure 2 shown. Among them, the filter 3 is used to filter the X-ray and filter out stray rays. The monochromator 4 is used to adjust the energy of the X-ray. The specimen stage 5 is used to fix the raw nacre samples and each of the processed products. The X-ray detector 6 is used to collect the projection images of the raw nacre samples and each of the processed products.

[0066] In an exemplary embodiment, an insert 2 can also be set in the micro-CT system. The insert 2 is located between the X-ray source 1 and the filter 3, as Figure 2 shown. The insert 2 is an optional accessory or module for enhancing the system function of the micro-CT system, adapting to specific experimental requirements, or optimizing the imaging effect. For example, various optical devices. Through the insert 2, the application range of the micro-CT system can be expanded, making it applicable to more complex samples or experimental conditions.

[0067] Step S3: According to the number of the projection images, three-dimensional image reconstruction is performed using the phase retrieval algorithm and the iterative reconstruction algorithm to generate three-dimensional data; the three-dimensional data includes a phase contrast micro-CT three-dimensional reconstruction image and the corresponding three-dimensional voxel matrix.

[0068] In this embodiment, in step S3, according to a plurality of the projection images, a three-dimensional image reconstruction is performed using a phase retrieval algorithm and an iterative reconstruction algorithm to generate three-dimensional data, which specifically includes the following steps.

[0069] Step S31: According to a plurality of the projection images, a phase retrieval algorithm is used to reconstruct the refractive index distributions of the raw nacre and each of the processed products.

[0070] Step S32: According to the refractive index distributions of the raw nacre and each of the processed products, a three-dimensional CT reconstruction is performed using an iterative reconstruction algorithm to generate the three-dimensional data of the raw nacre and each of the processed products. Among them, the iterative reconstruction algorithm used is the FDK (Feldkamp Davis Kress) algorithm.

[0071] In an exemplary embodiment, before step S31 in which, according to a plurality of the projection images, a phase retrieval algorithm is used to reconstruct the refractive index distributions of the raw nacre and each of the processed products, the non-destructive quality evaluation method of nacre based on three-dimensional structural porosity further includes an image preprocessing process, which specifically includes the following steps.

[0072] Step S30: Geometric correction and noise filtering are respectively performed on each of the projection images to obtain preprocessed projection images; the preprocessed projection images are used as the projection images to reconstruct the refractive index distributions of the raw nacre and each of the processed products based on the phase retrieval algorithm.

[0073] Step S4: According to the three-dimensional data, a pore segmentation is performed using an image segmentation algorithm, and the porosities of the raw nacre and each of the processed products are calculated.

[0074] In this embodiment, step S4 performs a pore segmentation using an image segmentation algorithm according to the three-dimensional data, and calculates the porosities of the raw nacre and each of the processed products, which specifically includes the following steps.

[0075] Step S41: According to the three-dimensional data, an image segmentation algorithm is used to extract a pore-matrix binary three-dimensional structure model. Among them, the image segmentation algorithm is the Otsu (Otsu threshold segmentation) algorithm or an image segmentation algorithm based on a U-Net deep learning model.

[0076] Step S42: Based on the pore-matrix binary three-dimensional structure model, the pore volumes and the total sample volumes of the raw nacre and each of the processed products are determined.

[0077] Step S43: According to the pore volumes and the total sample volumes of the raw nacre and each of the processed products, the porosities of the raw nacre and each of the processed products are calculated.

[0078] Step S5, determining the quality grade of the raw mother-of-pearl product and each of the processed products according to the porosity of the raw mother-of-pearl product and each of the processed products and combining the relationship among porosity, calcination temperature and sample quality.

[0079] This embodiment takes into account the close correlation between porosity, calcination temperature and sample quality. Generally, the higher the calcination temperature of the processed product of raw mother-of-pearl, the higher its porosity, and the higher the corresponding sample quality; the lower the calcination temperature of the processed product of raw mother-of-pearl, the lower its porosity, and the lower the corresponding sample quality. Therefore, this embodiment starts from the perspective of calcination temperature and porosity, and obtains processed products with different processing degrees by calcining raw mother-of-pearl at various calcination temperatures, and calculates the porosity of raw mother-of-pearl and each processed product, so that according to the porosity of raw mother-of-pearl and each processed product and the calcination temperature, combined with the relationship between porosity, calcination temperature and sample quality, the quality grade of raw mother-of-pearl and each processed product can be non-destructively evaluated.

[0080] In an exemplary embodiment, the quality grades of raw mother-of-pearl and its processed products include high grade, medium grade and low grade. Among them, the value range of porosity corresponding to high grade is: ε>40%; the value range of calcination temperature corresponding to high grade is: T>800℃. The value range of porosity corresponding to medium grade is: 5%≤ε≤40%; the value range of calcination temperature corresponding to medium grade is: 400℃≤T≤800℃. The value range of porosity corresponding to low grade is: ε<5%; the value range of calcination temperature corresponding to low grade is: T<400℃. Among them, ε is porosity and T is calcination temperature.

[0081] In order to make the technical solution of this embodiment clearer, the specific implementation process of the technical solution of this embodiment is described in detail below in the form of examples. The specific implementation steps are as follows.

[0082] (1) Raw mother-of-pearl and its calcined products.

[0083] In this embodiment, the raw pearl mother-of-pearl product is selected from the pearl oyster family, the pearl oyster Pteria martensii The shells of Dunker were washed and crushed but not calcined as experimental raw materials. Then the polished raw pearl mother-of-pearl was placed in an integrated box-type resistance furnace of model KSW-6-12ASP for calcination, and heated at a heating rate of 10℃ / min in air. According to the requirements of the Pharmacopoeia of the People's Republic of China and the TG (thermogravimetric analysis) experiment, the program temperature rise process was from room temperature to 400℃, 600℃, and 800℃, respectively. After 1h, it was taken out and placed in a dryer for cooling. Finally, the processed products at 400℃, 600℃, and 800℃ were obtained by calcination, which were named MC400, MC600, and MC800 respectively.

[0084] (2) Micro-CT scanning.

[0085] In this embodiment, a micro-CT system is used to conduct X-ray micro-CT experiments. As Figure 2 shown, the micro-CT system includes an X-ray source 1 for emitting X-rays, and a filter 3, a monochromator 4, a specimen stage 5, and an X-ray detector 6 arranged in sequence along the direction of the X-rays.

[0086] In this embodiment, the specimen stage 5 is a five-axis precision specimen stage with five-dimensional movement directions. It includes a swivel table and a rotary table arranged above the swivel table. Its movement directions include the left-right dimension, up-down (lifting) dimension, pitch swing dimension, left-right swing dimension, and rotary table rotation dimension of the swivel table.

[0087] In this embodiment, the optimal experimental parameters for the X-ray micro-CT experiment using the micro-CT system are obtained through theory and experiments. This embodiment conducts X-ray micro-CT experiments at Shanghai Funan Scientific Instruments Co., Ltd. Finally, the optimal experimental parameters for the X-ray micro-CT experiment are determined as follows: the energy of the X-rays is 75 - 85 keV, the X-ray detector 6 uses a CCD (Charge Coupled Device) with an effective pixel size of 25 μm, the single-projection exposure time of the X-rays is 500 ms, and the SOD (distance from the sample to be measured to the X-ray detector 6) is set to 12 mm. Specifically, for the raw nacre, the scanning voltage is 75 kV, the exposure time is 330 ms, the scanning average number is 8, the SOD is 12.26 mm, the scanning time is 86 min, and the scanning pixel is 2.5 μm; for MC400, the scanning voltage is 84 kV, the exposure time is 606 ms, the scanning average number is 8, the SOD is 12.26 mm, the scanning time is 103 min, and the scanning pixel is 2.5 μm; for MC600, the scanning voltage is 84 kV, the exposure time is 606 ms, the scanning average number is 10, the SOD is 12.26 mm, the scanning time is 126 min, and the scanning pixel is 2.5 μm; for MC800, the scanning voltage is 75 kV, the exposure time is 330 ms, the scanning average number is 6, the SOD is 12.26 mm, the scanning time is 69 min, and the scanning pixel is 2.5 μm.

[0088] In the X-ray micro-CT experiment, the projection images need to be obtained according to the following standardized operation procedures: The raw nacre and each processed product and other samples to be measured are accurately fixed on the five-axis precision specimen stage of the micro-CT system respectively, and a 180° full-circle uniform rotation is carried out with the vertical axis as the rotation reference. The micro-focus X-ray source (voltage: 30 - 100 kV, current: 50 - 200 μA) and the high-resolution flat panel detector (pixel size: ≤50 μm) are synchronously triggered, and two-dimensional projection images are continuously obtained using an equal-angle sampling strategy as a set of projection images. These projection images are used as the original input for 3D reconstruction, so as to generate 3D data with isotropic voxels through the FDK algorithm, including the phase-contrast micro-CT 3D reconstruction images with sub-micron resolution and the corresponding 3D voxel matrix, and this 3D data can characterize the 3D structures of the raw nacre and the processed products.

[0089] (3) Image processing, 3D image reconstruction, and porosity calculation of the projection images.

[0090] The specific process of using the projection images for phase recovery and slice reconstruction in this embodiment includes: First, geometric correction and noise filtering are performed on the original projection images to eliminate systematic errors and random noise; Subsequently, a phase recovery algorithm is used to extract the phase information of the raw nacre and each processed product from the projection images, and the refractive index distributions of the raw nacre and each processed product are reconstructed; Finally, the phase-enhanced projection data is reconstructed into 3D data with isotropic voxels through the FDK algorithm, including the phase-contrast micro-CT 3D reconstruction images with sub-micron resolution and the corresponding 3D voxel matrix, thereby generating high-resolution 3D tomographic slice images.

[0091] When quantitatively characterizing the pore morphological parameters in this embodiment, an image segmentation algorithm, such as the Otsu algorithm or the image segmentation algorithm based on the U-Net deep learning model, is used to perform threshold segmentation on the 3D tomographic slice images. In this embodiment, the CTAn analysis software is used to perform threshold segmentation on the 3D tomographic slice images (3D images), the Otsu algorithm is used to distinguish the nacre layer and the pores, and a pore-matrix binary 3D structure model is extracted. Based on the pore-matrix binary 3D structure model, the pore volume and the total sample volume of the raw nacre and each processed product are obtained, and the pore volume and the total sample volume of the raw nacre and each processed product are substituted into the porosity calculation formula, and quantitative analysis is carried out using the porosity calculation formula to calculate the porosities of the raw nacre and each processed product.

[0092] In this embodiment, the pore-matrix dualistic three-dimensional structure model is a simplified characterization system established based on three-dimensional data. The internal structure of the raw nacre and each processed product is divided into a pore phase (cavity or fluid-filled region) and a matrix phase (solid skeleton). The extraction process includes: first, preprocessing the original three-dimensional data by noise reduction and gray-scale normalization, then performing threshold segmentation of the image using the Otsu algorithm or an image segmentation algorithm based on the U-Net deep learning model, and finally optimizing the quality of the pore-matrix dualistic three-dimensional structure model through morphological operations and connected component analysis. This pore-matrix dualistic three-dimensional structure model directly provides basic data for porosity calculation, including the pore volume (V1) and the total sample volume (V2) of the raw nacre and each processed product. Among them, the pore volume (V1) and the total sample volume (V2) correspond to the number of voxels marked as the pore phase and the overall matrix in the pore-matrix dualistic three-dimensional structure model respectively. Thus, by substituting the pore volume (V1) and the total sample volume (V2) into the porosity calculation formula, the porosity of the raw nacre and each processed product can be calculated.

[0093] In this embodiment, the porosity is the ratio of the pore volume to the total sample volume, expressed as a percentage. The porosity calculation formula is: ε = V1 / V2 × 100%; where ε is the porosity, V1 is the pore volume, and V2 is the total sample volume.

[0094] The porosity results of the raw nacre and each processed product calculated in this embodiment are shown in Table 1.

[0095] Table 1 Porosity results of the raw nacre and each processed product

[0096] It can be seen from Table 1 that during the calcination process of raw nacre, there is a significant relationship between the porosity of nacre, the calcination temperature, and the sample mass, which is specifically as follows: As the calcination temperature increases from raw nacre (uncalcined) to 800 °C, the porosity increases from 0.2541% to 45.8760%, indicating that high-temperature calcination promotes the decomposition of organic components and the reorganization of the mineral structure, forming more pores. At the same time, the mass decreases due to the loss of volatile substances, and the porosity is negatively correlated with the mass loss. The classification of the quality grade needs to take the porosity as the core index and comprehensively judge by combining data verification (such as correcting outliers) and physicochemical properties (such as composition, hygroscopicity), resulting in the following quality grade judgment methods: High-grade (such as MC800, porosity > 40%) is fully calcined and has a crispy texture, which is conducive to the release of active ingredients; medium-grade (MC600, porosity 5% - 40%) is moderately calcined; low-grade (raw nacre and MC400, porosity < 5%) is undercalcined. In practical applications, multiple indicators such as calcium content and appearance can also be supplemented for refined grading, so as to ensure scientificity and practicality.

[0097] Figures 3 to 6 It is a three-dimensional schematic diagram of the reconstructed three-dimensional structure obtained by reconstructing the two-dimensional projection diagrams of raw nacre and three processed products along the X, Y, and Z axes. The X-axis is the cross-section, the Y-axis is the longitudinal section, and the Z-axis is the longitudinal profile. Among them, Figure 3 is the three-dimensional schematic diagram of raw nacre. Figure 4 is the three-dimensional schematic diagram of raw nacre calcined at 400 °C for 1 h. Figure 5 is the three-dimensional schematic diagram of raw nacre calcined at 600 °C for 1 h. Figure 6 is the three-dimensional schematic diagram of raw nacre calcined at 800 °C for 1 h. By comparing Figure 3 , Figure 4 , Figure 5 and Figure 6 , it can be seen that the higher the calcination temperature, the more and larger the pores in the three-dimensional structure, and the higher the porosity.

[0098] This embodiment proposes a non-destructive evaluation method for the quality of nacre based on the porosity of the three-dimensional structure. First, the raw nacre is calcined by the open calcination method to obtain processed products with different processing degrees. Then, according to the brightness changes when X-rays penetrate the raw nacre and the processed products with different processing degrees, the parameters for image acquisition by the micro-CT system are determined, and the raw nacre and its processed products with different processing degrees are sequentially scanned by micro-CT to obtain multiple sets of projection images. Then, by analyzing the multi-angle projection data (projection images) and using the phase recovery algorithm to reconstruct the refractive index distributions of the raw nacre and its processed products with different processing degrees, combined with the iterative reconstruction algorithm, three-dimensional data is finally obtained, including the three-dimensional reconstructed image of phase contrast micro-CT and the corresponding three-dimensional voxel matrix. Then, based on the above three-dimensional data, a pore-matrix binary three-dimensional structure model is extracted by an image segmentation algorithm, and a method for calculating the porosity of pore morphology parameters is used, that is, the porosity calculation formula is used to calculate the porosities of the raw nacre and its processed products with different processing degrees, realizing the quantitative characterization of the micro-structure. Finally, according to the porosities of the raw nacre and its processed products with different processing degrees, combined with the relationship between porosity, calcination temperature and sample quality, the sample quality of the raw nacre and its processed products with different processing degrees is judged. The sample quality characterizes the processing degrees (fully calcined, moderately calcined, under-calcined) of the processed products of the raw nacre, providing a reference for the subsequent classification of quality grades. This embodiment uses micro-CT scanning based on X-rays to non-destructively obtain the three-dimensional micro-structures of the raw nacre and its different processed products, and then quantitatively evaluate the quality of nacre according to the porosity of the three-dimensional micro-structure, realizing efficient, accurate, rapid and non-destructive quality evaluation.

[0099] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0100] Specific examples are used in this article to elaborate on the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, based on the idea of this application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A non-destructive evaluation method for nacre quality based on the porosity of three-dimensional structure, characterized in that The non-destructive evaluation method for the quality of nacre based on the porosity of three-dimensional structure includes: Calcining the raw nacre at various calcining temperatures by the open calcination method to obtain multiple processed products with different processing degrees; Performing micro-CT scans on the raw nacre and each of the processed products respectively to obtain a number of projection images; Based on the number of projection images, using the phase retrieval algorithm and the iterative reconstruction algorithm to perform three-dimensional image reconstruction to generate three-dimensional data; the three-dimensional data includes the phase contrast micro-CT three-dimensional reconstructed image and the corresponding three-dimensional voxel matrix; Based on the three-dimensional data, using the image segmentation algorithm to perform pore segmentation, and calculating the porosity of the raw nacre and each of the processed products; Based on the porosity of the raw nacre and each of the processed products, combining the relationship among porosity, calcining temperature and sample quality, to determine the quality grades of the raw nacre and each of the processed products.

2. The non-destructive evaluation method of nacre quality based on the porosity of the three-dimensional structure according to claim 1, wherein Performing micro-CT scans on the raw nacre and each of the processed products respectively to obtain a number of projection images, specifically including: Determining the micro-CT scan parameters of the micro-CT system according to the brightness change of the X-ray when the X-ray penetrates the raw nacre and each of the processed products; Based on the micro-CT scan parameters, using the micro-CT system to perform micro-CT scans on the raw nacre and each of the processed products respectively to obtain the projection images of the raw nacre and each of the processed products.

3. The non-destructive evaluation method for nacre quality based on the porosity of three-dimensional structure according to claim 2, wherein, The micro-CT system includes an X-ray source for emitting X-rays, and a filter, a monochromator, a specimen stage and an X-ray detector arranged in sequence along the direction of the X-ray; The filter is used to filter the X-rays to remove stray rays; The monochromator is used to adjust the energy of the X-rays; The specimen stage is used to fix the raw nacre and each of the processed products; The X-ray detector is used to collect the projection images of the raw nacre and each of the processed products.

4. The non-destructive evaluation method for nacre quality based on the porosity of the three-dimensional structure according to claim 1, characterized in that, Based on the number of projection images, using the phase retrieval algorithm and the iterative reconstruction algorithm to perform three-dimensional image reconstruction to generate three-dimensional data, specifically including: Based on the number of projection images, using the phase retrieval algorithm to reconstruct the refractive index distribution of the raw nacre and each of the processed products; Based on the refractive index distribution of the raw nacre and each of the processed products, using the iterative reconstruction algorithm to perform three-dimensional CT reconstruction to generate the three-dimensional data of the raw nacre and each of the processed products.

5. The non-destructive evaluation method of nacre quality based on the porosity of three-dimensional structure according to claim 4, characterized in that, Before the step of reconstructing the refractive index distribution of the raw nacre and each of the processed products using the phase retrieval algorithm based on the number of projection images, the non-destructive evaluation method for the quality of nacre based on the porosity of three-dimensional structure further includes: Performing geometric correction and noise filtering on each of the projection images respectively to obtain the preprocessed projection images; the preprocessed projection images are used as the projection images to reconstruct the refractive index distribution of the raw nacre and each of the processed products based on the phase retrieval algorithm.

6. The method for non-destructive evaluation of nacre quality based on the porosity of the three-dimensional structure according to claim 4, wherein The iterative reconstruction algorithm is the FDK algorithm.

7. The non-destructive evaluation method for nacre quality based on the porosity of three-dimensional structure according to claim 1, characterized in that Based on the three-dimensional data, using the image segmentation algorithm to perform pore segmentation, and calculating the porosity of the raw nacre and each of the processed products, specifically including: Based on the three-dimensional data, an image segmentation algorithm is used to extract the pore-matrix binary three-dimensional structure model; Based on the pore-matrix binary three-dimensional structure model, determine the pore volume and the total sample volume of the raw nacre and each of the processed products; According to the pore volume and the total sample volume of the raw nacre and each of the processed products, calculate the porosity of the raw nacre and each of the processed products.

8. The non-destructive evaluation method for nacre quality based on the porosity of three-dimensional structure according to claim 7, characterized in that, The image segmentation algorithm is the Otsu algorithm or an image segmentation algorithm based on the U-Net deep learning model.

9. The non-destructive evaluation method of nacre quality based on the porosity of three-dimensional structure according to claim 7, characterized in that The following formula is used to calculate the porosity of the raw nacre and each of the processed products: ε = V1 / V2×100%; where ε is the porosity, V1 is the pore volume, and V2 is the total sample volume.

10. The method for non-destructive evaluation of nacre quality based on the porosity of three-dimensional structure according to claim 1, wherein, The quality grades include high grade, medium grade, and low grade; The value range of the porosity corresponding to the high grade is: ε > 40%; The value range of the calcination temperature corresponding to the high grade is: T > 800°C; The value range of the porosity corresponding to the medium grade is: 5% ≤ ε ≤ 40%; The value range of the calcination temperature corresponding to the medium grade is: 400°C ≤ T ≤ 800°C; The value range of the porosity corresponding to the low grade is: ε < 5%; The value range of the calcination temperature corresponding to the low grade is: T < 400°C; where ε is the porosity and T is the calcination temperature.

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