LA-ICP-MS-based micro-damage test method for gold content and thickness of plating layer of gold-plated silver ornament

Abstract

The invention relates to the technical field of metal coating determination, and discloses an LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP-MS. The LA-ICP- Step 2, performing laser ablation on the ablation area for multiple times, and generating corresponding sample aerosol in each ablation; step 3, carrying out denudation analysis on five gold standard samples with gradient gold contents, analyzing the contents of impurity elements in the plating layer through a standard curve method, summing the contents of the impurity elements, and then carrying out subtraction to calculate the gold content of the plating layer; and 4, when the Ag element content detected in the step 3 is exponentially increased for the first time compared with the Ag content analyzed after previous denudation and is larger than 0.1%, denudation is stopped, the denudation frequency is determined, and the coating thickness is calculated through a coating thickness measurement model. According to the testing method, accurate, efficient and micro-damage testing of the gold-plated and silver-plated ornament is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of metal coating measurement, and particularly relates to a micro-destructive testing method for the gold content and thickness of the coating on gold-plated and silver-plated ornaments based on LA-ICP-MS. Background Art

[0002] In today's jewelry consumer market, gold-plated and silver-plated ornaments occupy a certain share due to their unique advantages. These ornaments have silver as the substrate and are plated with a layer of gold on the outside. Compared with pure gold ornaments, they have the significant characteristic of high cost performance. The content and thickness of the gold coating are directly related to the price of gold-plated and silver-plated ornaments. Therefore, it is particularly crucial to accurately measure the gold content and thickness of the coating on gold-plated and silver-plated ornaments.

[0003] Currently, for the measurement of the gold content and thickness of the coating on gold-plated and silver-plated ornaments, mainly technical means such as X-ray fluorescence spectrometry (XRF) and scanning electron microscopy (SEM) are used. Among them, scanning electron microscopy (SEM) can directly measure the gold content and thickness of the coating and has high accuracy. However, this method has obvious drawbacks. It requires cutting and sample preparation of the sample, which will undoubtedly cause irreversible damage to such precious samples as gold-plated and silver-plated ornaments, making the SEM method not very suitable for such samples in practical applications.

[0004] On the other hand, X-ray fluorescence spectrometry (XRF) measures the fluorescence intensity generated by the mass number of metal elements per unit area, and then calculates the gold content and thickness of the coating based on the density of the metal coating. The advantage of this method is that it does not require sample destruction and sample preparation, but it also faces many limitations. Due to the influence of various factors such as the matrix material and the coating material, the XRF method has great limitations in measuring the thickness of the coating on gold-plated and silver-plated ornaments and is difficult to truly meet the requirements of accurate testing.

[0005] In view of the above problems, the present application provides a micro-destructive testing method for the gold content and thickness of the coating on gold-plated and silver-plated ornaments based on LA-ICP-MS to perform accurate, efficient, and micro-destructive testing. Summary of the Invention

[0006] The present invention aims to provide a micro-destructive testing method for the gold content and thickness of the coating on gold-plated and silver-plated ornaments based on LA-ICP-MS to achieve accurate, efficient, and micro-destructive testing of the coating thickness and gold content.

[0007] To achieve the above object, the present invention adopts the following technical solution: A micro-destructive testing method for the gold content and thickness of the coating on gold-plated and silver-plated ornaments based on LA-ICP-MS, comprising the following steps:

[0008] Step 1: Clean and dry the surface of the sample to be tested, and determine a flat ablation area;

[0009] Step 2: Perform laser ablation on the eroded area multiple times, and generate corresponding sample aerosols for each ablation.

[0010] Step 3: Perform ablation analysis on 5 gold standard samples with a gradient of gold content, and then analyze the content of impurity elements in the coating by the standard curve method, mainly including elements such as Cu, Ag, and Fe.

[0011] Sum up the contents of each impurity element and then perform subtraction to calculate the gold content of the coating.

[0012] Step 4: When the content of Ag element detected in Step 3 shows an exponential increase for the first time compared with the Ag content analyzed after the previous ablation, and the content of Ag element is greater than 1‰, stop ablation, determine the number of ablation times, and calculate the coating thickness through the measurement model of the coating thickness.

[0013] The principle and advantages of this solution are as follows:

[0014] 1. High test accuracy: This solution uses LA-ICP-MS technology to perform laser ablation on the eroded area multiple times. The laser has the characteristic of high energy density and can accurately ablate the coating layer by layer. By controlling the energy and pulse number of the laser, the ablation depth can be accurately controlled. Each ablation generates corresponding sample aerosols, and the main elements Cu, Ag, and Fe in the coating are quantitatively analyzed by the standard curve method. When the content of Ag element is suddenly detected to increase exponentially and the content is greater than 1‰, stop ablation. This is because the gold-plated and silver jewelry is based on silver, and detecting a high content of silver means that the gold coating has been penetrated to reach the substrate. Based on the clear mathematical relationship between the ablated volume and the element concentration, combined with parameters such as the coating density, the coating thickness measurement model can accurately calculate the coating thickness. At the same time, the LA-ICP-MS technology has extremely high detection sensitivity for elements and can accurately determine the gold content of the coating. Compared with the XRF method, it avoids the interference of complex factors such as the substrate material on the measurement; compared with the SEM method, it does not need to damage the sample, reducing the possibility of artificially introducing errors, so it can greatly improve the accuracy of the test results.

[0015] 2. Improved test efficiency: In the existing technology, due to the influence of various factors such as the substrate material and the coating material, the XRF method may need to adjust the measurement parameters, replace different filters or collimators, etc. multiple times during the measurement process to minimize interference, which results in a long test time for a single sample, usually several minutes or even longer. The SEM method not only requires a complex cutting and sample preparation process, and the sample preparation time may be up to several hours, but also during the imaging and analysis process, it is necessary to perform multiple scans and focus adjustments on different parts of the sample, further increasing the test time.

[0016] After the sample aerosol is generated by laser ablation, LA-ICP-MS can simultaneously detect multiple ions in the aerosol. Through the mass analyzer of the mass spectrometer, ions with different mass-to-charge ratios can be monitored at the same time, such as ions corresponding to elements like Fe, Ag, Cu, etc. This means that all target elements in the aerosol generated by a single laser ablation operation can be analyzed synchronously, without the need to measure each element separately or perform multiple scans like traditional methods. At the same time, the data acquisition and processing speed of this technology is extremely fast. Modern advanced LA-ICP-MS equipment can collect a large number of data points per second, complete the analysis of the element content of the coating in a short time, and quickly calculate the coating thickness and gold content in combination with a pre-established measurement model. Under ideal conditions, the test time for a single sample can be shortened to 10 seconds, greatly improving the test efficiency compared with XRF and SEM methods, and meeting the requirements of batch detection.

[0017] 3. Micro-damage to gold-plated ornaments: The existing SEM method cuts and prepares samples, which causes irreversible damage to precious samples such as gold- and silver-plated ornaments, seriously affecting the integrity and value of the samples. During the laser ablation process of this solution, the energy of the laser beam is highly concentrated in a tiny area. By precisely controlling laser parameters such as energy density, pulse width, and frequency, precise evaporation of the coating material can be achieved. The size of the micro-pits formed by each laser ablation is extremely small, usually in the order of dozens of micrometers in diameter and only nanometers to micrometers in depth. Compared with the overall size of the sample and the coating thickness, this kind of damage is extremely small. For common gold- and silver-plated ornaments with a coating thickness of a few micrometers, the single laser ablation depth may be only a fraction of a micrometer. Moreover, the ablation area is generally selected at a position on the surface of the ornament that relatively does not affect the aesthetics and overall performance. Compared with the cutting damage of the SEM method, the degree of micro-damage of this solution to the ornament can be ignored, protecting the integrity and value of the sample to the greatest extent while ensuring the test is carried out, and meeting the special requirements for the detection of precious gold- and silver-plated ornaments.

[0018] Further, the measurement model is specifically:

[0019] f(x) = 0.662x + 4.690

[0020] Where x is the number of ablation times when the coating disappears, and f(x) is the coating thickness, with the unit of μm.

[0021] Beneficial effects: The above measurement model clearly establishes a quantitative relationship between the number of erosion times \(x\) when the coating disappears and the coating thickness \(f(x)\). In step 4, when it is detected that the content of Ag element suddenly increases exponentially and the content is greater than 1‰, it is determined that the substrate is eroded, and then the erosion stops. After determining the number of erosion times \(x\), the coating thickness can be accurately calculated based on this model. Compared with the traditional measurement method, this model uses a clear mathematical formula to greatly improve the accuracy of coating thickness measurement. Moreover, the measurement model focuses on the key and easily obtainable parameter of the number of erosion times. By fitting coefficients and constants through a large amount of experimental data, it fundamentally avoids complex interference factors such as the substrate and coating materials. It simplifies the complex actual measurement problem into the counting of the number of erosion times and mathematical operations. As long as the number of erosion times is determined strictly in accordance with the specified process during the test, the coating thickness can be accurately obtained, significantly improving the measurement accuracy and better meeting the requirements for accurate testing of the coating thickness of gold and silver plated ornaments.

[0022] Secondly, the measurement model provides a clear and simple calculation method for the entire test process. In actual operation, the tester only needs to determine the number of erosion times \(x\) according to the steps, and then substitute it into the model \(f(x)=0.662x + 4.69\) for simple multiplication and addition operations to quickly obtain the coating thickness result. This greatly simplifies the originally complex thickness measurement process, reduces the overly high requirements for the tester's professional knowledge and operation skills, enables more ordinary technicians to accurately perform the test tasks, and improves the operability of the test work.

[0023] Furthermore, since the model only depends on the basic parameter of the number of erosion times, it is not affected by the specific styles, shapes of gold and silver plated ornaments, and the specific material differences between the coating and the substrate. Whether it is a simple-shaped gold and silver plated necklace or a complex-shaped gold and silver plated bracelet, as long as it conforms to the basic category of gold and silver plated ornaments, the coating thickness can be accurately calculated through this model. This universality enables this test method to be widely applied to the detection of various gold and silver plated ornaments, improves the application range and practical value of the test method, and is of great significance for the quality control of different product lines of production enterprises and the sampling inspection work of diverse gold and silver plated ornaments by market supervision departments.

[0024] Furthermore, the method for establishing the measurement model includes the following steps:

[0025] Step A: Divide multiple independent erosion areas on the surface of the sample, and perform different numbers of erosions on different erosion areas;

[0026] Step B: Use an optical profiler to scan all the erosion areas on the surface of the sample and synthesize a three-dimensional topography image of the scan, and then measure the erosion depths of different erosion areas;

[0027] Step C: Perform data fitting on the erosion times and erosion depths of different erosion regions to obtain a measurement model.

[0028] Beneficial effects: The above measurement model is obtained through multi-region data collection, accurate erosion depth measurement, and scientific data fitting. On the one hand, it fully considers the diversity of the sample surface. The surface of gold and silver-plated ornaments may be uneven, and there may be differences in the coating thickness and material distribution at different parts. When testing gold and silver-plated ornaments with complex shapes or obvious surface differences, multi-region erosion and measurement can collect and analyze data according to the characteristics of different parts. For example, for gold and silver-plated ornaments with carvings or concave-convex textures on the surface, the erosion data of different regions can reflect the different performances of the coatings at the textured and flat parts during the erosion process, enabling the measurement model to better adapt to such complex samples and improving the accuracy and effectiveness of the test results.

[0029] Secondly, whether it is gold and silver-plated ornaments produced by traditional processes or new processes, a measurement model adapted to them can be established through this method. This greatly enhances the adaptability of the test method to products with different production processes, is beneficial for market supervision departments to detect diversified products and production enterprises to control the quality of products with different processes, and improves the versatility and practicality of the test method.

[0030] Furthermore, in the above step 1, the laser wavelength used for erosion is 213 nm, the energy is 50%, the pulse frequency is 10 Hz, the spot size is 60 - 70 μm, and the erosion speed is 5 - 25 μm / s.

[0031] Beneficial effects: The 213 nm laser can erode the coating more stably, avoiding phenomena such as local over-erosion or under-erosion caused by concentrated or unevenly distributed energy, making the sample aerosol generated after each erosion more consistent in composition. Setting the energy at 50% controls the erosion amount within a small range while ensuring effective erosion of the coating, making the action of the laser on the coating mild and controllable, and avoiding the instantaneous erosion of a large amount of coating due to too high energy. The smaller erosion amount means that the change in the coating after each erosion is subtle, which is more conducive to accurately grasping the relationship between the erosion process and the coating thickness.

[0032] Secondly, by coordinating parameters such as a pulse frequency of 10 Hz, a spot size of 60 - 70 μm, and an ablation rate of 5 - 25 μm / s, the laser ablation process was jointly optimized, further ensuring a uniform and fine ablation effect. The 10 Hz pulse frequency avoids the instantaneous energy accumulation caused by overly dense pulses, enabling the laser energy to act uniformly on the coating surface, reducing the influence of thermal stress on the coating, and ensuring the uniformity of ablation. The 60 - 70 μm spot size can not only cover an appropriate ablation area but also control the ablation range, avoiding unnecessary interference with the surrounding area and ensuring that the ablation amount per time is small and stable. The ablation rate of 5 - 25 μm / s can be flexibly adjusted according to the actual situation of the coating, and uniform and fine ablation can be achieved for coatings of different thicknesses and materials.

[0033] Further, in steps 2 and 3, after elemental analysis of the sample aerosol obtained after each ablation, the next laser ablation is carried out.

[0034] Beneficial effects: Timely elemental analysis after each ablation can monitor the ablation process in real time. In step 4, by detecting that the Ag element content is greater than 1‰, it is determined whether the substrate has been ablated, and then the ablation is stopped and the coating thickness is calculated. During the ablation process, real-time elemental analysis allows testers to understand the changes in the content of various impurity elements in the coating in a timely manner. When approaching the substrate, the increasing trend of the Ag element content can be detected earlier, thus more accurately determining the timing to stop ablation. Compared with the previous method of analyzing only after multiple ablations, which may cause deviations in the calculation of the coating thickness due to over-ablation, the new method can greatly improve the accuracy of measuring the coating thickness. When measuring a relatively thin coating, real-time monitoring of the ablation process can avoid thickness measurement errors caused by minor ablation differences, ensuring that the measurement results are closer to the actual coating thickness.

[0035] Further, when performing laser ablation in step 2, the sample to be tested is placed in a helium atmosphere.

[0036] Beneficial effects: Helium has extremely high thermal conductivity. When the laser acts on the surface of the coating of a silver-gilt jewelry, a large amount of heat is generated. Helium can quickly carry away this heat, achieving efficient heat dissipation, and effectively preventing the sample from undergoing structural changes or damage due to local overheating. During the ablation process, excessive temperature may cause the gold coating to melt, deform, and even affect the properties of the substrate silver. The rapid heat dissipation effect of helium maintains the original state of the sample, ensuring the stability of the ablation process. At the same time, a stable temperature environment is conducive to the more uniform action of laser energy on the coating, further optimizing the ablation effect, making the composition of the sample aerosol generated after each ablation more consistent, and laying a good foundation for the subsequent accurate analysis of the coating element content.

[0037] Meanwhile, the low density and high fluidity of helium enable it to quickly carry away the ablation products generated during the ablation process. If the debris and vapor generated by ablation remain on or near the sample surface, they may interfere with the subsequent laser ablation process, resulting in uneven ablation. Moreover, these residual substances may also affect the composition of the sample aerosol, causing deviations in the elemental analysis results. The rapid purging of ablation products by helium ensures that each laser ablation is performed on a relatively clean sample surface, improving the uniformity of ablation, effectively excluding the interference of impurities in the ablation products, and enabling the detection results to more accurately reflect the actual elemental composition of the coating.

[0038] Further, in step 3, the sample aerosol needs to be ionized before elemental content analysis.

[0039] Beneficial effects: The ionization process converts neutral sample aerosol particles into charged ions, which will generate stronger response signals in the electric or magnetic field of the detection instrument. Compared with non-ionized aerosols, ionized samples can be detected more sensitively during detection, greatly reducing the detection limit and enabling the discovery of the presence of trace elements, providing more powerful technical support for accurate analysis of the elemental content of the coating and helping to more comprehensively and meticulously understand the composition of the coating.

[0040] Further, in step 3, the five gradients of the gold standard sample are respectively 99%, 99.9%, 99.99%, 99.999% gold content, among which the 99.9% gold content includes two gradients, and the impurity content ranges from 0.04% to 0.08%.

[0041] Beneficial effects: The above settings refine the gradient settings of the gold standard sample, covering a wider range of gold purities, enabling the standard sample to more comprehensively simulate various gold content situations that may occur in actual gold-plated and silver-plated ornaments, enhancing the adaptability of the test method to complex coating situations, and greatly expanding the applicable range of the analysis method.

[0042] Meanwhile, for the 99.9% gold content, two different impurity content gradients are set, and the impurity content ranges from 0.04% to 0.08% ， Taking into account the differences in impurity content in the actual coating. Different impurity contents will affect the properties and elemental analysis of the coating. By setting these two gradients, the interference of impurities in the actual sample can be more accurately reflected, further improving the representativeness of the standard sample and thus enhancing the accuracy of the analysis results. Description of the Drawings

[0043] Figure 1 It is a line graph showing the change of Ag element content with the number of ablation times in the embodiment of the present invention.

[0044] Figure 2Schematic diagram of the morphology of the embodiment of the present invention after 2 and 15 times of stripping. DETAILED DESCRIPTION

[0045] The following is further described in detail through specific implementation methods:

[0046] The reference numerals in the drawings of the specification include: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

[0047] The embodiment is basically as shown in the attached Figure 1 - Figure 2 As shown:

[0048] The micro-destructive testing method for the gold content and thickness of the gold-plated silver jewelry based on LA-ICP-MS includes the following steps:

[0049] Step 1: Clean and dry the surface of the sample to be tested and determine a flat ablation area.

[0050] Step 2: Perform multiple laser ablation on the ablation area, and generate corresponding sample aerosol each time; during ablation, the sample to be tested is placed in a helium atmosphere. Helium has extremely high thermal conductivity, and can quickly take away the heat during the ablation process, achieving efficient heat dissipation and effectively avoiding structural changes or damage to the sample due to local overheating.

[0051] Step 3, perform stripping analysis on 5 gold standard samples with gradient gold content, obtain the element content of gold samples with different gold contents as a reference curve, and then analyze the content of impurity elements in the coating by the standard curve method, mainly including elements such as Cu, Ag and Fe; then sum and subtract the content of each impurity element to calculate the gold content of the coating. The sample aerosol needs to be ionized before element content analysis; and the sample aerosol obtained after each stripping is subjected to elemental analysis before the next laser stripping. The standard curve method is a commonly used method for quantitative analysis and will not be described here.

[0052] The gold standard sample is a sample made entirely of gold, without any other matrix. The five gradients of the gold standard sample are 99%, 99.9%, 99.99%, and 99.999% gold content, of which 99.9% gold content includes two gradients, and the impurity content ranges from 0.04-0.08%.

[0053] Step 4: When the Ag content detected in step 3 increases exponentially for the first time compared to the Ag content analyzed after the last stripping, and the Ag content is greater than 1‰, stop stripping, determine the number of stripping times, and calculate the coating thickness through the coating thickness measurement model. The specific expression of the measurement model is:

[0054] f(x)=0.662x+4.690

[0055] Where x is the number of erosion times when the coating disappears, and f(x) is the coating thickness in μm.

[0056] This embodiment also provides a coating thickness measurement model for gold and silver plated ornaments, including the following steps:

[0057] Step A: Select 4 independent samples, and divide 5 flat, clean and independent erosion areas on the surface of each sample, including Area 1 to Area 5. Use LA-ICP-MS to erode different erosion areas for different numbers of times, which are 2 times, 3 times, 4 times, 10 times and 15 times respectively.

[0058] Step B: Use an optical profiler (OCM) to scan all the erosion areas on the sample surface, use a data processing algorithm to synthesize a three-dimensional topography image of the scanned surface, realize the measurement of any structural size on the three-dimensional topography, and then measure the erosion depth of different erosion areas to obtain the results in Table 1.

[0059] Table 1 Erosion depths corresponding to different erosion times

[0060]

[0061] Appendix Figure 2 The following shows the topography results after 2 times and 15 times of erosion, the plan view (a) and three-dimensional view (b) after 2 times of erosion; the plan view (c) and three-dimensional view (d) after 15 times of erosion; combined Figure 2 with Table 3, it can be seen that the erosion depth after 15 times of erosion is significantly greater than that after 2 times of erosion.

[0062] Step C: Use a computer to perform data fitting on the erosion times and erosion depths of different erosion areas to obtain a measurement model. The specific expression of the measurement model is:

[0063] f(x) = 0.662x + 4.690

[0064] Where x is the number of erosion times when the coating disappears, and f(x) is the coating thickness in μm.

[0065] The coefficient of determination (R-Square) of this measurement model is 0.99, which has a good fitting degree. It is obtained through LA-ICP-MS testing. As Figure 1 shown, after 1 - 7 times of erosion, the silver content in the coating does not exceed 3×10 -6。As the number of erosions increased from 7 to 13, the silver content gradually increased and showed a certain linear trend. After 14 and 15 erosions, the Ag content was much higher than that of the first 13 erosions and showed an exponential growth trend. Based on the above results, it can be concluded that after 13 erosion tests on the sample, the silver content increased sharply. Therefore, after 13 erosion tests, the coating basically disappeared, and then the substrate was gradually eroded. Therefore, the number of erosions when the coating of this silver-gold plated jewelry disappeared was 13 times, and its coating thickness was 13.30 μm after calculation according to the measurement model.

[0066] When the number of erosions when the coating disappeared was 1, its coating thickness was calculated to be 5.352 μm. Therefore, this model can accurately measure silver-gold plated jewelry with a coating thickness greater than 5.4 μm.

[0067] This embodiment also obtained the elemental content results of the coating in the silver-gold plated jewelry, as shown in Table 2:

[0068] Table 2 Gold content of silver-gold plated jewelry (LA-ICP-MS)

[0069]

[0070]

[0071] Comparative Example 1

[0072] The sample used in Comparative Example 1 was from the same batch as the silver-gold plated jewelry used in the example. Four different parts, namely B1, B2, B3, and B4, were selected on the surface of the sample, and the gold content of the four parts of the sample was tested using EDXRF and the average value was taken. The results are shown in Table 3. It can be seen from the results that the gold content of the silver-gold plated jewelry is between 811.6‰ and 929.8‰. According to the requirements of GB11887, the gold content in pure gold jewelry should be greater than 990‰. By testing the gold content in silver-gold plated jewelry using EDXRF, the gold content of all samples is less than 990‰, which does not meet the requirements of pure gold. At the same time, a relatively high silver content was found in the EDXRF results, with an average of about 100‰. Since the substrate of the silver-gold plated jewelry is silver, it is very likely that the low gold content is affected by the substrate, and the accuracy of the detection results is low.

[0073] Table 3 Gold content of silver-gold plated jewelry (EDXRF)

[0074]

[0075]

[0076] Among them, "-" represents less than the detection limit; the unit of each elemental content is ‰.

[0077] Comparative Example 2

[0078] The sample used in Comparative Example 1 and the gold-plated and silver-plated ornaments used in the examples belong to the same batch. After cutting and sample preparation of the gold-plated and silver-plated ornament samples, the samples were inlaid, and then polished successively with sandpapers of 120#, 240#, 320#, 400#, and 600#. The polishing time for each sandpaper was not more than 30 s, and the polishing direction was changed by 90° each time the sandpaper was replaced. Then, SEM was used to measure the coating thickness of the sample. Three representative cross-sections were selected for measurement. The measurement sites were relatively flat and the boundaries were obvious. The statistical results of the measurement results of the three regions are shown in the table. It can be seen from the results that by directly measuring the coating thickness of the sample using SEM, the average coating thickness of the sample is 14.89 μm.

[0079] Table 4 Gold content of gold-plated and silver-plated ornaments (SEM)

[0080]

[0081] In summary:

[0082] Compared with Comparative Example 1, the analysis of the coating element content obtained in the example is more accurate, less affected by the matrix material, and the test results are highly accurate.

[0083] Compared with Comparative Example 2, the coating thickness obtained by LA-ICP-MS in the example is 13.3 μm, and the coating thickness directly measured by scanning electron microscopy (SEM) is 14.89 μm. The deviation between the two results is 10.1%. Therefore, the measurement model of the coating thickness in the example has high accuracy.

[0084] This solution uses LA-ICP-MS technology to perform multiple laser ablations in the ablation area. Each ablation generates a corresponding sample aerosol, and then the aerosol is ionized. LA-ICP-MS technology is used to analyze the main elements Cu, Ag, Fe, etc. in the coating. When the Ag content analyzed after the previous ablation shows an exponential increase for the first time and is greater than 1‰, the ablation is stopped. This is because the gold-plated and silver-plated ornaments are based on silver, and detecting a high content of silver means that the gold coating has been penetrated to reach the matrix. Based on the clear mathematical relationship between the ablated volume and the element concentration, combined with parameters such as the coating density, a coating thickness measurement model is constructed, which can accurately calculate the coating thickness. At the same time, LA-ICP-MS technology has extremely high detection sensitivity for elements and can accurately determine the gold content of the coating. Compared with the XRF method, it avoids the interference of complex factors such as the matrix material on the measurement; compared with the SEM method, it does not require sample destruction and reduces the possibility of artificially introducing errors, so it can greatly improve the accuracy of the test results.

[0085] Secondly, during the laser ablation process, the energy of the laser beam is highly concentrated in a tiny area. The size of the micro-pits formed by each laser ablation is extremely small, usually in the order of dozens of micrometers in diameter, and the depth is only in the range of nanometers to micrometers. Compared with the overall size of the sample and the thickness of the coating, this kind of damage is extremely tiny and has negligible impact on the ornament. While ensuring the progress of the test, it maximally protects the integrity and value of the sample, meeting the special requirements for the detection of precious gold and silver plated ornaments.

[0086] The above are only embodiments of the present invention, and common general technical solutions and / or characteristics in the solutions are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application shall be subject to the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A micro-damage test method for the gold content and thickness of gold-plated silver jewelry based on LA-ICP-MS, characterized in that: The following steps are involved: Step 1: Clean and dry the surface of the sample to be tested to determine a flat erosion area; Step 2, performing laser ablation on the ablation area for multiple times, and generating corresponding sample aerosol each time; Step 3, performing stripping analysis on 5 gold standard samples with a gradient of gold content, and then analyzing the content of impurity elements in the coating by the standard curve method, mainly including elements such as Cu, Ag and Fe; The content of each impurity element is summed up and then subtracted to calculate the gold content of the coating; Step 4: When the Ag content detected in step 3 increases exponentially for the first time compared with the Ag content analyzed after the last stripping, and the Ag content is greater than 1‰, stop stripping, determine the number of stripping times, and calculate the coating thickness through the coating thickness measurement model.

2. The micro-damage testing method for the gold content and thickness of the gold-plated silver jewelry based on LA-ICP-MS according to claim 1 is characterized in that: The measurement model is specifically: f(x)=0.662x+4.690 Where x is the number of times the coating disappears, and f(x) is the coating thickness in μm.

3. The micro-damage testing method for the gold content and thickness of the gold-plated silver jewelry based on LA-ICP-MS according to claim 2 is characterized in that: The method for establishing the measurement model comprises the following steps: Step A, dividing the sample surface into multiple independent erosion areas, and performing different erosion times on different erosion areas; Step B, using an optical profilometer to scan all the eroded areas on the sample surface and synthesize the scanned three-dimensional topography image, and then measure the erosion depth of different eroded areas; Step C: fitting the data of the denudation times and denudation depths of different denudation areas to obtain a measurement model.

4. The micro-damage testing method for the gold content and thickness of the plating layer of gold-plated silver jewelry based on LA-ICP-MS according to claim 1 is characterized in that: In the step 1, the laser wavelength used for ablation is 213 nm, the energy is 50%, the pulse frequency is 10 Hz, the spot size is 60-70 μm, and the ablation speed is 5-25 μm / s.

5. The micro-damage testing method for the gold content and thickness of the plating layer of gold-plated silver jewelry based on LA-ICP-MS according to claim 1 is characterized in that: In step 2 and step 3, the sample aerosol obtained after each ablation is subjected to elemental analysis before the next laser ablation is performed.

6. The micro-damage testing method for the gold content and thickness of the gold-plated silver jewelry based on LA-ICP-MS according to claim 6 is characterized in that: When laser ablation is performed in step 2, the sample to be tested is placed in a helium atmosphere.

7. The micro-damage testing method for the gold content and thickness of the gold-plated silver jewelry based on LA-ICP-MS according to claim 6 is characterized in that: In step 3, the sample aerosol needs to be ionized before element content analysis.

8. The micro-damage testing method for the gold content and thickness of the plating layer of gold-plated silver jewelry based on LA-ICP-MS according to claim 7, characterized in that: In step 3, the five gradients of the gold standard sample are respectively 99%, 99.9%, 99.99%, and 99.999% gold content, wherein the 99.9% gold content includes two gradients, and the impurity content ranges from 0.04 to 0.08%.

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