A Composite Method for Characterizing the Migration Substances and Coating Loss of Nano-Ceramic Cookware

Abstract

The present invention belongs to the identification and detection of kitchen utensils, especially the detection of kitchen utensils with nano-material coatings. A composite method for characterizing the migration substances and coating loss of nano-ceramic cookware, including the detection of specific metal migration amount: First, simulate the aging under working conditions, use 4% acetic acid simulant to maintain for two hours at 98 °C, and analyze the dissolution amount of target elements in the soaking solution using an inductively coupled plasma emission spectrometer; the detection of coating residues: including the detection of heavy metal content in the residues and the detection of residue particle size. The method of the present invention is comprehensive and reasonable, with a clever concept. The effect of simulated aging can peel the coating from the cookware substrate, simulate the extreme conditions of food production during cooking, detect the migration amount of corresponding harmful substances in the coating during daily cooking, and can quickly and accurately analyze the content of corresponding elements at one time, with high precision and good reproducibility. And accurately observe the changes in the coating thickness, roughness and nano-particle size distribution during the aging process of the cookware.

Description

Technical Field

[0001] The present invention belongs to the identification and detection of kitchen utensils, especially the detection of kitchen utensils with nano-material coatings. Background Art

[0002] Nanometer (nm), the transliteration of nanometer, is a millimicron and a unit of length measurement. The symbol of the International System of Units is nm. Nano-technology is a newly emerging technology that developed rapidly in the early 1990s. Its ultimate goal is for humans to directly manipulate individual atoms and molecules according to their own consciousness to manufacture products with specific functions, and it is considered the high point of the development of science and technology in the 21st century. The nano-level refers to fine particles with a size between 1 nm and 100 nm. Nano-materials can be defined as materials in which the composition phase or grain structure is controlled to a length size below 100 nm. It can also be said that the average particle size or structural size of nano-materials is within 100 nm. Due to the unique chemical, physical, and biological properties of nano-materials, it has extremely broad application prospects in the fields of electronics, chemical engineering, machinery, biomedicine, etc.

[0003] The "nano food contact materials" have emerged for only over a decade, but their development speed is extremely astonishing. The so-called "nano food contact materials" refer to a general term for a class of materials that apply nano-technology and use nano-composite materials to perform nano-synthesis, nano-addition, and nano-modification on food contact products, so that the food contact materials have super functions or strange characteristics [1].

[0004] Nano-ceramics is a composite material manufactured by introducing nano-level ceramic particles, whiskers, fibers, etc. into the ceramic matrix to improve the performance of the ceramics. It improves the room-temperature mechanical properties of the matrix material, improves the high-temperature properties, and this material has machinability and superplasticity. It densifies and homogenizes the composition structure of the ceramic material, improves the performance of the ceramic material, and enhances its use reliability [2]. Nano-ceramic coated non-stick kitchen utensils mainly include two types: wok and soup pot for stove heating. The ceramic materials used to manufacture these products include silicon dioxide nano-particles, titanium dioxide nano-particles, and nano-clay. These nano non-stick cookware are sold to consumers as substitutes for polytetrafluoroethylene coated non-stick products [3]. Kitchen utensils products with nano-ceramic coatings attached to the metal surface by processes such as plasma spraying, electrophoretic deposition, thermal chemical reaction, and micro-arc oxidation. Such nano-ceramic coated kitchen utensils have the advantages of easy washing, wear resistance, high temperature resistance, acid and alkali corrosion resistance, superhydrophobic antibacterial properties [4] [5], etc. However, the risk of nano-molecules migrating from these new engineering nano-molecular food contact materials into food to consumers has emerged increasingly [5].

[0005] Currently, there is no relevant detection for nano-ceramic coated kitchen utensils in China, which belongs to a blank field. Summary of the Invention

[0006] The object of the present invention is to simulate the working conditions of imported nano-ceramic non-stick cookware purchased on the market, study the heavy metal migration under different wear degrees, as well as the content of heavy metals and the distribution of nano-scale particles in the ceramic coating powder obtained by friction under simulated working conditions, and provide a composite method for characterizing the migration substances and coating loss of nano-ceramic cookware.

[0007] The technical solution adopted by the present invention to achieve the above object is: a composite method for characterizing the migration substances and coating loss of nano-ceramic cookware, including the detection of specific metal migration amount and the detection of coating residues.

[0008] The detection of the specific metal migration amount: First, simulate the working condition aging, respectively simulate the wear of the coating surface by using a spatula to stir-fry during cooking and tools during cleaning the cookware, select 2 years as the full life cycle, and detect the cookware in the states of brand new, used for 6 months, 12 months, 18 months, and 24 months respectively; during the detection, use 4% acetic acid mimic at 98 °C for two hours, and use an inductively coupled plasma optical emission spectrometer to analyze the dissolution amount of target elements in the soaking solution [8].

[0009] The detection of the coating residues: includes the detection of heavy metal content in the residues and the detection of the particle size of the residues. Among them, the detection of heavy metal content in the residues: The coating residues peeled off due to friction during the simulated aging test of the cookware are subjected to microwave digestion treatment of the samples using a nitric acid-hydrofluoric acid-hydrogen peroxide system, and according to the ICP-OES reference working conditions in Appendix A of GB 31604.49-2016 National Food Safety Standard for Food Contact Materials and Articles - Determination of Arsenic, Cadmium, Chromium, Lead and Determination of the Migration Amounts of Arsenic, Cadmium, Chromium, Nickel, Lead, Antimony, and Zinc [8], an inductively coupled plasma optical emission spectrometer is used to analyze the elements of the samples.

[0010] The detection of the particle size of the residues: The coating residues peeled off from the substrate surface by friction are analyzed for particle size using a laser particle size analyzer to detect the particle size distribution of nano-elements in the coating.

[0011] Furthermore, the detection of the coating residues also includes the detection of the roughness of the residues: It is to analyze the roughness of the aged ceramic coating of the cookware using a 3CCD true-color confocal microscope (HYBRID C3).

[0012] Furthermore, the detection of the coating residues also includes the detection of coating loss: Observe the wear condition of the coating of the cookware subjected to the aging test under a 500-fold objective lens of a metallurgical microscope (AxioVert.A1).

[0013] Preferably, for the digestion treatment, microwave digestion is carried out using a nitric acid - hydrofluoric acid - hydrogen peroxide system with a volume ratio of 5:2:1. The sample weighing is 0.1 - 0.5 g. The microwave digestion furnace is maintained at 150 - 180 °C for 6 - 10 minutes, and then heated to 200 °C and maintained for 30 - 45 minutes. After cooling, it is heated on a hot plate to drive off the acid until nearly dry. The coating residue sample is rinsed, transferred, and fixed volume to a 50 mL volumetric flask with nitric acid solution (5 + 95). According to the ICP - OES reference working conditions in Appendix A of GB 31604.49 - 2016 National Food Safety Standard - Determination of Arsenic, Cadmium, Chromium, Lead and Determination of Migration Amounts of Arsenic, Cadmium, Chromium, Nickel, Lead, Antimony, Zinc in Food Contact Materials and Articles [8], the sample is tested on the machine, and the test instrument uses an inductively coupled plasma optical emission spectrometer manufactured by Thermo Fisher Scientific for elemental analysis.

[0014] Preferably, for the detection of the residue particle size: Mie scattering theory is adopted, with a refractive index of 1.52, an injection pump speed of 50 - 60%, a test dispersant of water, a laser echo power of 100%, and a detected particle size range of 0.01 - 3800 μm. The coating residue peeled from the substrate surface by friction is analyzed for particle size using a laser particle size analyzer.

[0015] The advantages of the method of the present invention are as follows: 1. The aging test uses real materials that come into contact with the coating surface during daily cooking and cleaning of cookware, such as a chicken wing wooden spatula / spoon for stir - frying and serving soup, a scouring pad for scrubbing the cookware. The reciprocating device of the linear grinding instrument is used to simulate the working conditions of cooking / cleaning the cookware, and the counterweight is used to simulate the operator's force. The effect of the simulated aging can peel the coating from the cookware substrate, and the aging time and aging degree can be well controlled. When the program is set, the experimenter can leave the test site without affecting the progress of other work.

[0016] For the quantitative analysis of the migration amounts of seven elements such as arsenic, cadmium, chromium, nickel, lead, antimony, and zinc, 4% acetic acid simulant is used and maintained at 98 °C for two hours, which can well simulate the extreme conditions of food ingredient production during cooking and ensure that the migration amounts of the corresponding harmful substances in the coating during daily cooking are below the experimental values. Using an inductively coupled plasma optical emission spectrometer to analyze the target elements in the soaking solution can quickly and accurately analyze the content of the corresponding elements at one time, with high precision and good reproducibility. The pretreatment method for the detection of seven heavy metals in the coating stripping has the advantages of small reagent consumption, short digestion time, thorough sample digestion, and little indirect pollution to the environment. The treated sample has few impurities and does not contaminate the injector of the inductively coupled plasma optical emission spectrometer, with the advantages of extending the service life of the instrument and reducing the frequency and difficulty of daily maintenance.

[0017] Observing the coating surface with a metallurgical microscope can intuitively detect the thickness change of the coating during the aging process of the cookware. The observation position is accurate, the requirements for sample preparation are simple, and the generation of solid waste is reduced.

[0018] The 3CCD true-color confocal microscope can intuitively analyze the roughness change of the cookware coating, can perform non-destructive testing, and the generated 3D simulation effect diagram can quickly judge the overall shape and detailed conditions of the worn surface. Description of the Drawings

[0019] Figure 1 It is the diagram of the metal element migration law of the Zwilling 32cm ceramic non-stick long-handle frying pan

[0020] Figure 2 It is the diagram of the metal element migration law of the CHEF TOPF ceramic-coated non-stick milk pan

[0021] Figure 3 It is the diagram of the metal element migration law of the BERNDES ceramic-coated non-stick frying pan

[0022] Figure 4 It is the particle size distribution diagram of the Zwilling 32cm ceramic non-stick long-handle frying pan

[0023] Figure 5 It is the particle size distribution diagram of the CHEF TOPF 18cm ceramic-coated milk pan

[0024] Figure 6 It is the particle size distribution diagram of the Berndes Balance 24cm ceramic non-stick frying pan

[0025] Figure 7 It is the metallographic diagram of the Berndes Balance 24cm ceramic non-stick frying pan at 6 months

[0026] Figure 8 It is the metallographic diagram of the Berndes Balance 24cm ceramic non-stick frying pan at 12 months

[0027] Figure 9 It is the metallographic diagram of the Berndes Balance 24cm ceramic non-stick frying pan at 18 months

[0028] Figure 10 It is the metallographic diagram of the Berndes Balance 24cm ceramic non-stick frying pan at 24 months

[0029] Figure 11 It is the metallographic diagram of the Berndes Balance 24cm ceramic non-stick frying pan at 30 months

[0030] Figure 12 It is the unaged metallographic diagram of the Zwilling 32cm ceramic non-stick long-handle frying pan

[0031] Figure 13 is the metallographic diagram of Zwilling 32cm ceramic non-stick long handle frying pan for 24 months

[0032] Figure 14 is the unaged metallographic diagram of CHEF TOPF 18cm ceramic coated milk pan

[0033] Figure 15 is the metallographic diagram of CHEF TOPF 18cm ceramic coated milk pan for 24 months

[0034] Figure 16 is the unaged metallographic diagram of Berndes Balance 24cm ceramic non-stick frying pan

[0035] Figure 17 is the metallographic diagram of Berndes Balance 24cm ceramic non-stick frying pan for 24 months

[0036] Figure 18 is the microscopic diagram of Berndes Balance 24cm ceramic non-stick frying pan for 24 months

[0037] Figure 19 is the microscopic diagram of CHEF TOPF 18cm ceramic coated milk pan for 24 months

[0038] Figure 20 is the microscopic diagram of Zwilling 32cm ceramic non-stick long handle frying pan for 24 months. Specific embodiments

[0039] The present invention will be further described in detail below in conjunction with specific embodiments, but the present invention is not limited to specific embodiments.

[0040] Embodiment 1: A composite method for characterizing the migration substances and coating loss of nano-ceramic cookware, including the detection of specific metal migration amount and the detection of coating residues,

[0041] 1. The detection of the specific metal migration amount: It is an experiment on the specific metal migration amount of cookware under simulated working conditions. This experiment aims to study the specific migration law of harmful heavy metals in nano-ceramic coated cookware under working conditions. In the experiment, the accelerated aging method is used to detect the specific metal migration amount of the target cookware at different stages of the whole life cycle.

[0042] 1.1 Simulation of the aging test

[0043] The aging test used a linear grinding instrument from TABER Company in the United States [6] to linearly rub the coating on the surface of the cooking utensils using special wingwood spatula friction heads and scouring pad friction heads respectively, so as to simulate the wear of the coating surface by the tools during the use of spatulas for stir-frying and cleaning the cookware in cooking. According to the product introduction and relevant information, the service life of non-stick pans is between 1 and 2 years. We selected 2 years as the full life cycle and tested them in the states of brand new, 6 months of use, 12 months of use, 18 months of use, and 24 months of use respectively.

[0044] Estimation of cooking time: Cooking is carried out twice a day, with a net operation time of 10 minutes each time using the cooking utensils. Operating 300 days a year, the total cumulative time in two years is 12000 minutes.

[0045] Estimation of washing time: Cleaning is carried out twice a day, with a net operation time of 1 minute each time. Operating 300 days a year, the total cumulative time in two years is 1200 minutes.

[0046] After observation and summary, the actual manual stir-frying and washing operation frequency is 30 times per minute in one direction.

[0047] Settings of the linear grinding instrument: Use a friction head with a diameter of 2 feet, apply a counterweight mass of 600 g, and the friction frequency is 60 reciprocations per minute (120 times per minute in one direction). Therefore, the program settings are as follows (Table 1):

[0048] Table 1. Experimental simulation aging conditions Unit: times (one direction)

[0049]

[0050] 1.2 Selection of specific migration test conditions and methods

[0051] Quantitative analysis was carried out on the migration amounts of seven elements including arsenic, cadmium, chromium, nickel, lead, antimony, and zinc. The experimental conditions referred to the research results of Hu Mingsheng et al. [7] and referred to GB 4806.4-2016 "National Food Safety Standard - Ceramic Products". Using 4% acetic acid simulant to maintain for two hours at 98 °C, the target elements in the soaking solution were analyzed using an inductively coupled plasma emission spectrometer [8]. It has been proven that using an inductively coupled plasma emission spectrometer to determine the dissolution amounts of various metal elements in the non-stick pan coating is a detection method with simple operation, high speed, accuracy, and high method stability, which better meets the requirements of production and daily laboratory analysis.

[0052] 1.3 Migration law of specific migration amount

[0053] Under the above simulated working conditions and aging conditions, specific migration amount tests of seven elements including arsenic, cadmium, chromium, nickel, lead, antimony, and zinc were carried out on three selected non-stick pans with nano-ceramic coatings on the inner walls. The results are as follows (see Table 2)

[0054] Table 2. Specific migration amounts of seven metal elements in the aging test of cookware under simulated working conditions Unit: mg / L

[0055]

[0056] The calculation and expression of the results should reflect the volume ratio (S / V) of the actual contact area of the cookware to the food simulant under foreseeable use conditions. In the specific migration amount test for the first use of the above three cookware, the contact areas S were 1.02 dm2, 1.77 dm2, and 3.14 dm2 respectively. When the aging test was carried out, the areas of the actual wound surfaces were calculated according to the friction head travel of the linear grinder as 0.21 dm2, 0.28 dm2, and 0.28 dm2 respectively. In the experiment, for the three cookware in the state of intact coating, 4% acetic acid simulant with the same soaking volume as above was used to carry out five 2-hour soaks at 98 °C respectively to simulate the background values of the specific migration amounts of 7 metal elements at 0 months, 6 months, 12 months, 18 months, and 24 months when the coating was not aged. According to the data, the specific migration amounts of 7 metal elements in the three cookware did not change significantly during the five soaks, and no values of the specific migration amounts of the 7 metal elements in the intact coating reached the quantification limit. Therefore, although the aging contact area was smaller than the total contact area of the soaking solution during the aging test, the influence of the undamaged contact area on the migration amount could be ignored. According to the experimental results, a regular graph of the specific migration amounts of seven metal elements in three non-stick cookware with nano-ceramic coatings during the use time of 0 - 24 months was drawn (see Figures 1-3 )

[0057] It can be seen from the migration regular graph that during the 0 - 24 month usage cycle of the three cookware, the specific migration amounts of all target elements did not show an obvious increasing trend due to the aging of the nano-ceramic coating, and the test results of the migration amounts of all target elements were lower than the limits of the specific migration amounts of elements in the GB 4806 series of national standards

[0058] 2. Detection of the coating residue

[0059] 2.1 Detection of heavy metal content in the residue

[0060] Heavy metals such as Pb, Cr, and Cd will be deposited in bones, fat and other tissues after being ingested by the human body. Trace intake will not cause harm to human functions in a short period of time, but long-term accumulation will cause irreversible damage to the nervous system. This section tests the content of common heavy metals in the coating residues peeled off due to friction during the simulated aging test of ceramic coated kitchenware. The main components of the coating are inorganic silicon, titanium, aluminum and other components after wavelength dispersive X-ray fluorescence spectrometer, X-ray diffractometer and infrared spectroscopy analysis. The test instrument uses the inductively coupled plasma emission spectrometer manufactured by Thermo Fisher Scientific for elemental analysis. Due to the high content of inorganic silicon in the coating residues, the pretreatment process refers to the digestion treatment method of soil. The digestion conditions were optimized by referring to the relevant content of different digestion methods for determining the content of heavy metals in soil by Zhang Surong et al.

[10] . Finally, nitric acid-hydrofluoric acid-hydrogen peroxide system (volume ratio 5:2:1) was selected for microwave digestion. The sample weight was 0.25g, and the microwave digestion oven was kept at 180℃ for 6 minutes, then heated to 200℃ and kept for 30 minutes. After cooling, it was heated on an electric hot plate to drive out the acid until it was almost dry. The sample was rinsed with nitric acid solution (5+95) and transferred to a 50mL volumetric flask. Refer to GB 31604.49-2016 The samples were tested on the ICP-OES using the reference working conditions in Appendix A of the National Food Safety Standard for Determination of Arsenic, Cadmium, Chromium, Lead and Migration of Arsenic, Cadmium, Chromium, Nickel, Lead, Antimony and Zinc in Food Contact Materials and Products [8] (RF power: 1100-1500W; observation mode: axial observation or bidirectional observation; atomizer flow rate: 0.7-1.0L / min; auxiliary gas flow rate: 0.5-1.5L / min; plasma gas flow rate: 12L / min; pump speed: 0.75-1.25mL / min). The test results are as follows (Table 3):

[0061] Table 3. Contents of 7 elements in the friction residues of three kinds of cookware Unit: mg / kg

[0062]

[0063] As can be seen from the above results, the contents of Cr, Ni, Sb, and Zn in the friction residues of the Zwilling 32 cm ceramic non-stick long-handle frying pan have reached very high values. The contents of Cr, Ni, Pb, Sb, and Zn in the friction residues of the CHEF TOPF 18 cm ceramic-coated milk pan have reached very high values. The contents of Cr and Zn in the friction residues of the Berndes Balance 24 cm ceramic non-stick frying pan have also reached very high values. One of the important factors is that the pot body substrate of the Zwilling 32 cm ceramic non-stick long-handle frying pan is made of stainless steel, and some substrate residues are brought in during the friction process. Susana Addo Ntim [3] and others studied related nano-ceramic coating products. Through scanning electron microscopy combined with X-ray energy spectrometer analysis, the coating materials mainly contain compounds such as aluminum and silicon, and also contain inorganic salts such as Fe, Mn, Cr, and Ni. Based on product information, data verification, and analysis using various means such as infrared spectroscopy, we believe that such products may be non-stick coatings obtained by reconstructing glaze with clay, water, various inorganic minerals (such as kaolin, mullite, and feldspar), and various metal oxides. This feature is particularly obvious in the Zwilling 32 cm ceramic non-stick long-handle frying pan. This also proves from another perspective the reason for the relatively high content of some elements such as Cr.

[0064] 2.2 Detection of the nanoparticle distribution in the coating residues was carried out using a laser particle size analyzer (ANALYSETTE 28, Fritsch, Germany). The Mie scattering theory was adopted, with a refractive index of 1.52, an injection pump speed of 60%, a test dispersant of water, a laser echo power of 100%, and a detection particle size range of 0.01 - 3800 μm. The coating residues peeled from the substrate surface by friction were analyzed for particle size using a laser particle size analyzer. The test results are as Figures 4-6 , and the summary of the particle size distribution results is as follows (Table 4):

[0065] Table 4. Statistical table of the particle size distribution of the residues of the ceramic coatings of three pots after friction

[0066]

[0067] From the particle size distribution results, it can be seen that the content of nano-scale (1 - 100 nm) particles in the peeled coatings of the three pots is between 0.65% and 1.95%. The proportion of nano-scale particles in the powder is Berndes Balance 24 cm ceramic non-stick frying pan > CHEF TOPF 18 cm ceramic-coated milk pan > 32 cm ceramic non-stick long-handle frying pan. According to the component analysis, particles larger than 100 nm exist in the form of a blend of nano-ceramic compounds, other fillers, and binder materials in the coating. We will not discuss this in depth here. Example

[0068] On the basis of Example 1, further, the coating residue detection further includes residue roughness detection:

[0069] Meanwhile, the wear condition of the pot coating subjected to the aging test was observed under a 500x objective lens of a metallurgical microscope (Axio Vert.A1)

[11] .

[0070] First, the aging degree of a single Berndes Balance 24cm ceramic non-stick frying pan was explored. The coating thicknesses at 6 months, 12 months, 18 months, 24 months, and 30 months were observed under the microscope (see Figures 7-11 )

[0071] It was observed that during the first 12 months of use, the coating thickness did not change significantly and remained at 41μm. When it was used for 18 months, the coating thickness began to decrease to 39μm. When it was used for 24 months, the coating thickness began to decrease significantly to 34μm. When it was used for 30 months, the thickness had decreased to 31μm, which was 24.3% less than the original coating thickness. According to the research results of Stefano Rossi et al. [4], under the condition of 500 reciprocating frictions with a 1 kg pressure on the CS-10 friction head, the physical non-stick performance of the ceramic coating has decreased significantly. This may be because during the wear process of the nano-coating, the shear of asperities and the weakening of the "micro-bearing" effect of unmelted nanoparticles

[12]

[13] may occur, thus reducing its non-stick performance.

[0072] Secondly, the coating thicknesses of the three experimental pots were compared before aging and after 24 months of simulated aging (see Figures 12-17 ), and the following results (Table 5):

[0073] Table 5. Comparison of ceramic coating thicknesses of three pots after 24 months of aging

[0074]

[0075] On the basis of Examples 1 and 2, further, after the coating residue detection, a 3CCD true-color confocal microscope (HYBRID C3) was used to analyze the roughness of the ceramic coatings of the three pots after 24 months of aging

[14] (see Figures 18-20 )

[0076] The following results (Table 6):

[0077] Table 6. Comparison of roughness of ceramic coatings of three pots after 24 months of aging

[0078]

[0079] (*RSm is the average length of the roughness curve elements, which describes the overall trend of surface roughness. The larger the value, the rougher the surface. **Rz is the maximum height roughness, which describes the range of coating thickness under the corresponding test area. The larger the value, the greater the extreme unevenness of the surface.)

[0080] Analyzing the data from the simulation tests of the three cookware under aging test conditions, it is found that the coatings of all cookware have varying degrees of wear. From the prefabricated coating thickness (from high to low): Zwilling 32cm Ceramic Non-stick Long Handle Wok > CHEF TOPF 18cm Ceramic Coated Milk Pan > Berndes Balance 24cm Ceramic Non-stick Fry Pan. The wear rate (from high to low): Zwilling 32cm Ceramic Non-stick Long Handle Wok > Berndes Balance 24cm Ceramic Non-stick Fry Pan > CHEF TOPF 18cm Ceramic Coated Milk Pan. From the overall roughness level (from high to low): CHEF TOPF 18cm Ceramic Coated Milk Pan > Zwilling 32cm Ceramic Non-stick Long Handle Wok > Berndes Balance 24cm Ceramic Non-stick Fry Pan. The extreme unevenness in some areas (from high to low): Zwilling 32cm Ceramic Non-stick Long Handle Wok > CHEF TOPF 18cm Ceramic Coated Milk Pan > Berndes Balance 24cm Ceramic Non-stick Fry Pan.

[0081] From the above research, it can be seen that the nano-ceramic coated cookware has a stable and firm coating performance in the first 12 months of use, with good non-stick performance. At 18 months, the coating thickness shows a downward trend, and at 24 months, it has decreased significantly, the surface roughness has increased, and the non-stick performance has decreased significantly. During the 0 - 24 months of use cycle of the three cookware, the specific migration amounts of all target elements do not show an obvious increasing trend due to the aging of the nano-ceramic coating, and the test results of the specific migration amounts of all target elements are lower than the limits of the specific migration amounts of elements in the GB 4806 series of national standards.

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Claims

1. A composite method for characterizing the migration substances and coating loss of a nano-ceramic cookware, characterized in that: It includes the detection of specific metal migration and the detection of coating residues. The detection of specific metal migration: First, simulate the aging under working conditions, respectively simulate the wear of the coating surface by the spatula during cooking and the tools during the cleaning of the cookware. Select 2 years as the full life cycle, and detect the cookware in the states of brand new, used for 6 months, 12 months, 18 months, and 24 months respectively. During the detection, use 4% acetic acid simulant to keep for two hours at 98 °C, and use an inductively coupled plasma optical emission spectrometer to analyze the dissolution amount of target elements in the soaking solution. The detection of coating residues: It includes the detection of heavy metal content in the residues and the detection of residue particle size. Among them, the detection of heavy metal content in the residues: The coating residues peeled off due to friction during the simulated aging test of the cookware are treated by microwave digestion of the sample using a nitric acid-hydrofluoric acid-hydrogen peroxide system. According to the ICP-OES reference working conditions in Appendix A of GB 31604.49-2016 National Food Safety Standard Food Contact Materials and Products - Determination of Arsenic, Cadmium, Chromium, Lead and Determination of Migration Amounts of Arsenic, Cadmium, Chromium, Nickel, Lead, Antimony, Zinc, use an inductively coupled plasma optical emission spectrometer to analyze the elements of the sample. The detection of residue particle size: Use a laser particle size analyzer to analyze the particle size of the coating residues peeled off from the substrate surface by friction, and detect the particle size distribution of nano-elements in the coating.

2. A composite method for characterizing the migration and coating loss of a nano-ceramic cookware according to claim 1, characterized in that: The detection of coating residues also includes the detection of residue roughness: Use a 3CCD true color confocal microscope to analyze the roughness of the aged ceramic coating of the cookware.

3. A composite method for characterizing the migration and coating loss of a nano-ceramic cookware according to claim 1, characterized in that: The detection of coating residues also includes the detection of coating loss: Use a metallurgical microscope with a 500-fold objective lens to observe the wear of the cookware coating during the aging test.

4. A composite method for characterizing the migration and coating loss of a nano-ceramic cookware according to any one of claims 1-3, characterized in that: For the digestion treatment, perform microwave digestion using a nitric acid-hydrofluoric acid-hydrogen peroxide system with a volume ratio of 5:2:

1. Weigh 0.1 - 0.5 g of the sample, keep the microwave digestion furnace at 150 - 180 °C for 6 - 10 minutes, then raise the temperature to 200 °C and keep it for 30 - 45 minutes. After cooling, heat it on a hot plate to drive off the acid until nearly dry. Rinse and transfer the coating residue sample with nitric acid solution and make up the volume to 50 mL in a volumetric flask. According to the ICP-OES reference working conditions in Appendix A of GB 31604.49-2016 National Food Safety Standard Food Contact Materials and Products - Determination of Arsenic, Cadmium, Chromium, Lead and Determination of Migration Amounts of Arsenic, Cadmium, Chromium, Nickel, Lead, Antimony, Zinc, perform on-machine testing on the sample, and use an inductively coupled plasma optical emission spectrometer manufactured by Thermo Fisher Scientific to analyze the elements.

5. A method for characterizing the migration and coating loss of a nano-ceramic cookware, according to any one of claims 1-3, characterized in that: The detection of residue particle size: Adopt the Mie scattering theory, refractive index: 1.52, injection pump speed: 50 - 60%, test dispersant: water, laser echo power 100%, detection particle size range 0.01 - 3800 μm. Use a laser particle size analyzer to analyze the particle size of the coating residues peeled off from the substrate surface by friction.

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