A non-destructive method for determining the gold quality of thick layer gold-plated silver ornaments based on ultrasonic thickness measurement and application thereof

Abstract

The application belongs to the technical field of noble metal detection, and particularly relates to a non-destructive determination method for gold quality of thick-layer gold-plated silver ornaments based on ultrasonic thickness measurement and application thereof. i The method comprises the following steps: sample preparation; ultrasonic thickness measurement: obtaining thickness values d of each measurement point; surface area measurement; gold quality calculation: according to the obtained thickness values and surface area, the gold quality is calculated according to the following formula after calibration: wherein, ρ(Au) is the density of gold, d(avg) is the average thickness of the gold layer, S is the effective surface area of the ornament, K is a comprehensive correction coefficient (i=1 to n), and n is the total number of effective measurement points; and uncertainty evaluation. The method can accurately determine the gold quality in the thick-layer gold-plated ornament without destroying the ornament, is particularly suitable for the detection of thick-layer gold-plated silver jewelry, and has the advantages of wide measurement range, high accuracy and suitability for complex-shaped ornaments.

Description

Technical Field

[0001] This invention belongs to the field of precious metal testing technology, specifically relating to a non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement and its application. Background Technology

[0002] Gold-plated silver jewelry is a decorative precious metal product with a silver or silver alloy base and a gold or gold alloy layer plated on the surface. This invention primarily targets gold-plated silver jewelry made by depositing a thick gold layer on a silver substrate using electroplating technology, rather than the traditional gold-filled process. Thick-layer gold-plated silver jewelry combines the beautiful appearance of gold with the affordability of silver, and holds a significant market share in the jewelry industry.

[0003] With the development of the precious metals market, the demand for accurate determination of the gold content in gold-plated jewelry is increasing. Consumers, quality inspection agencies, and recycling companies all require a technical means to accurately and non-destructively determine the actual gold content in gold-plated jewelry. This is of great significance for product quality control, market supervision, consumer rights protection, and precious metal recycling pricing.

[0004] X-ray fluorescence spectrometry (XRF) is one of the most widely used methods for measuring coating thickness. This method excites the sample to generate characteristic X-rays, and then calculates the coating thickness and composition based on the fluorescence intensity. An XRF instrument emits a single X-ray to irradiate the sample surface, exciting each element in the sample to produce characteristic X-ray fluorescence. By detecting the energy and intensity of these characteristic X-rays, the elemental composition can be qualitatively analyzed, and the coating thickness can be quantitatively calculated.

[0005] However, this technology has the following limitations: (1) Upper limit of thickness detection: The detection accuracy of XRF method for thick layers (usually >7.5μm) drops significantly. This is because the penetration depth of a single X-ray is limited. When the coating thickness exceeds its effective detection range, the single X-ray signal of the substrate element is completely shielded, resulting in inaccurate measurement. (2) Inability to directly calculate mass: XRF method can only measure the coating thickness at local locations and cannot provide complete mass distribution information of the coating. (3) High equipment cost: High-precision XRF instruments are expensive (usually ranging from hundreds of thousands to millions of RMB), which limits its popularity among micro and small enterprises and individual operators. (4) Measurement area limitation: XRF measures the average thickness within the spot area (usually the spot diameter is 1-3mm), which has limitations for the comprehensive evaluation of complex-shaped jewelry.

[0006] Metallurgical microscopy is a destructive testing method that involves mounting, grinding, and polishing a sample, and then observing the cross-section of the coating using an optical microscope.

[0007] However, this technology has the following limitations: (1) Destructive: The sample must go through multiple processes such as cutting, setting, grinding, and polishing, and the jewelry cannot be restored, which is a destructive test. (2) Locality: It can only observe the local thickness of the cut section and cannot reflect the thickness distribution of the entire jewelry surface. (3) Arbitration property: This method is usually used as an arbitration benchmark and is not suitable for daily rapid testing.

[0008] The coulometric method is a method for calculating the thickness of a coating by electrolyzing and dissolving it.

[0009] However, this technology has the following limitations: (1) Semi-destructive: It requires local removal of the coating, which causes irreversible damage to the jewelry. (2) Shape limitation: For jewelry with complex openwork, inlay and other structures, the electrolyte is difficult to contact the entire coating surface evenly, and the measurement results are not representative. (3) Complex operation: It requires precise control of electrolysis parameters and high operating skills.

[0010] The gravimetric method includes two forms: the plating dissolution method and the differential weight method. The plating dissolution method involves immersing the jewelry in a solution that dissolves gold but not silver. After the gold plating layer is completely dissolved, the mass of the remaining substrate is weighed to calculate the mass of the gold. The differential weight method involves weighing the jewelry before and after plating, and calculating the mass of the gold plating layer based on the difference in mass.

[0011] However, this technology has the following limitations: (1) Destructive: The coating dissolution method requires destroying the integrity of the jewelry. (2) Not applicable to finished product inspection: The differential weight method is only applicable to online inspection during the production process and cannot be used for finished jewelry that has already been sold.

[0012] Ultrasonic thickness measurement technology has been widely used in the field of industrial non-destructive testing, mainly for measuring the thickness of metals, plastics, composite materials, etc. In recent years, ultrasonic technology has also been introduced into the field of coating thickness measurement. Patent CN105865380 discloses an ultrasonic coating thickness measurement device and method, which calculates the coating thickness by measuring the time difference of the echo signal at the interface between the coating and the substrate using an ultrasonic probe. This patent only focuses on the measurement of coating thickness and does not involve calculating the coating mass in conjunction with surface area. Patent CN103615996 discloses a method for improving the accuracy of coating thickness measurement by processing ultrasonic signals using spectrum analysis technology. This method also focuses only on thickness measurement and does not extend to mass calculation. Tian Gengfan et al. from the National Gemstone Testing Center conducted research on the detection of gold plating thickness in jewelry using ultrasonic microscopy (Precious Metals, 2021), verifying the feasibility of ultrasonic microscopy in detecting gold plating thickness. However, this research is limited to thickness analysis and does not involve methods for calculating gold mass in conjunction with surface area.

[0013] However, current technologies share the following common problems: 1. Insufficient thick-layer detection capability: XRF has limited accuracy in detecting thick gold plating (>10μm), failing to meet the accurate measurement requirements for thick gold-plated jewelry. 2. Lack of mass calculation: Existing methods (whether XRF, ultrasonic, or others) focus solely on plating thickness measurement, without establishing a complete technical solution from thickness measurement to mass calculation. 3. Difficulty in balancing non-destructive and high-precision methods: Non-destructive methods (such as XRF and ultrasonic) have lower accuracy and reliability than destructive methods (such as metallography and dissolution methods), making it difficult to meet the accuracy requirements for testing high-value jewelry. 4. Difficulty in handling complex shapes: For jewelry with complex geometric shapes, existing methods struggle to accurately measure the plating information across the entire area. Summary of the Invention

[0014] To address the problems existing in the prior art, the purpose of this invention is to design and provide a technical solution for a non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement and its application.

[0015] The present invention is specifically implemented using the following technical solutions: The first aspect of this invention provides a non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement, comprising the following steps: (1) Sample preparation: Clean the surface of the gold-plated silver jewelry to be tested to remove oil and impurities, check the surface condition and mark abnormal areas; (2) Ultrasonic thickness measurement: Select an ultrasonic probe of appropriate frequency to measure the gold layer thickness at multiple measurement points on the surface of the jewelry, and obtain the thickness value d at each measurement point. i ; (3) Surface area measurement: The effective surface area S of the ornament is measured by geometric measurement method, three-dimensional scanning method or drainage method; (4) Gold mass calculation: Based on the thickness and surface area obtained in steps (2) and (3), the gold mass is calculated according to the following formula after calibration: ; Where ρ(Au) is the density of gold, d(avg) is the average thickness of the gold layer, S is the effective surface area of ​​the jewelry, and K is the comprehensive correction coefficient. (i=1 to n), where n is the total number of valid measurement points; (5) Uncertainty assessment: perform uncertainty analysis on the gold quality measurement results and give the expanded uncertainty of the measurement results.

[0016] Furthermore, in step (2): When the gold plating thickness is 10-25μm, select a probe with a frequency of 100-200MHz; When the gold plating thickness is 25-50μm, select a probe with a frequency of 50-100MHz; When the gold plating thickness is 50-100μm, select a probe with a frequency of 15-50MHz; When the gold plating thickness is greater than 100μm, select a probe with a frequency of 5-15MHz.

[0017] Furthermore, the selection of the ultrasonic probe in step (2) includes any one or a combination of the following: Focusing probe, suitable for measuring samples on flat or gently curved surfaces; Delay block probes are suitable for thin-layer measurements or extending near-field lengths. Water immersion probe, suitable for complex shapes or batch measurements; Water spray probe, suitable for large samples that cannot be completely submerged.

[0018] Furthermore, step (2) uses the high-frequency pulse echo method to measure the gold layer thickness. The specific measurement steps include: S.1 emits ultrasonic pulses onto the gold surface; S.2 Acquire signals from surface echo and gold-silver interface echo; S.3 Measure the time interval Δt between the surface echo and the interface echo; S.4 According to the formula Calculate the gold layer thickness, where =3,240 m / s is the longitudinal wave velocity of the gold material.

[0019] Furthermore, in step (2): For jewelry with a regular shape, at least 5 measurement points should be evenly distributed on the surface; For jewelry with complex shapes, divide the jewelry into several functional areas, and select 3-5 representative measurement points for each functional area.

[0020] Furthermore, the thickness uniformity assessment in step (2) includes the following steps: according to the formula, (i=1 to n) Calculate the standard deviation sd of the thickness at each measurement point, according to the formula. Calculate the coefficient of variation (CV).

[0021] Furthermore, in step (3), the geometric measurement method is used to measure the S of regular-shaped ornaments, and the drainage method is used to measure the S of small, complex ornaments that cannot be three-dimensionally scanned. Both the geometric measurement method and the drainage method include the introduction of correction coefficients. The comprehensive correction coefficient K is calculated according to the following formula: ; in: Kp is the coating porosity correction coefficient, Kp=1-p, where p is the porosity; Kr is the surface roughness correction coefficient, K(r)=1+Ra / d(avg), where Ra is the arithmetic mean surface roughness; Ku is the thickness non-uniformity correction coefficient, K(u) = 1 + CV 2 CV is the thickness variation coefficient.

[0022] Furthermore, step (3) involves measuring the S-shape of the complex-shaped ornament using a three-dimensional scanning method, which includes the following steps: K.1 uses an optical 3D scanner to scan the jewelry from all angles to obtain 3D point cloud data; K.2 imports the scanned data into 3D processing software for processing and mesh generation; K.3 Calculate the surface area of ​​the mesh model.

[0023] Furthermore, the uncertainty assessment in step (5) includes: The thickness measurement uncertainty u(d) is evaluated and estimated using the standard deviation of multi-point measurements; The uncertainty of surface area measurement, u(S), is determined by the accuracy of the dimensional measurement. Evaluate the uncertainty of the correction coefficient u(K); Calculate the combined uncertainty uc; Taking the coverage factor k=2, calculate the expanded uncertainty U(m(Au)); The gold quality determination results are expressed as m(Au)±U(m(Au)).

[0024] A second aspect of the present invention provides the application of the method described above in the field of precious metal jewelry testing.

[0025] The present invention has the following beneficial effects: (1) Expanded measurement range: The present invention uses ultrasonic technology, which has better measurement accuracy than XRF method for thick gold plating (>10μm). When the gold plating layer exceeds 10μm, the XRF method has a significantly reduced measurement accuracy because the substrate signal is completely shielded; while the ultrasonic technology theoretically has no upper limit on the measurement range, and is particularly suitable for the accurate measurement of thick gold-plated jewelry.

[0026] (2) Direct calculation of gold mass: Existing ultrasonic coating thickness measurement technology can only measure the coating thickness and cannot calculate the total mass of gold. This invention innovatively establishes a complete technical solution of "thickness measurement + surface area measurement + mass calculation", realizing the leap from thickness measurement to mass calculation, and can directly give the total mass of gold in the jewelry.

[0027] (3) Completely non-destructive: The present invention does not damage the sample during the entire process of sample preparation, measurement and data processing. The jewelry can maintain its original shape and value, and can be repeatedly measured and verified. It is suitable for various scenarios such as consumer testing, judicial appraisal, and arbitration testing.

[0028] (4) Strong adaptability to complex shapes: By combining multiple surface area measurement methods (geometric measurement, three-dimensional scanning, drainage method), this invention can handle ornaments with various complex geometric shapes, including samples that are difficult to measure accurately by traditional methods such as hollow, inlaid, and chain-like shapes.

[0029] (5) Uncertainty assessment can be provided: This invention provides a complete method for assessing measurement uncertainty, which can give a reliability index of the measurement results, making it convenient for the use, comparison and traceability of the results.

[0030] (6) The equipment cost is relatively low: Compared with high-precision XRF instruments, the price of ultrasonic thickness gauges is usually in the range of tens of thousands to hundreds of thousands of yuan, which lowers the economic threshold for technology application and is conducive to its promotion and application in small and micro enterprises and grassroots quality inspection institutions.

[0031] (7) Verification can be performed in conjunction with XRF: The gold quality results determined by this invention can be cross-validated with the local thickness determined by XRF, thereby improving the confidence of the measurement results. For thick gold-plated jewelry where XRF measurement accuracy is relatively low, ultrasonic methods can provide more reliable quality data. Attached Figure Description

[0032] Figure 1 This is the overall flowchart; Figure 2 This is a schematic diagram illustrating the principle of ultrasonic thickness measurement. Figure 3 The waveform diagram of the ultrasonic echo signal at a typical measurement point; Figure 4 The waveform diagram of the ultrasonic echo signal at a typical measurement point; Figure 5 This is a flowchart of the three-dimensional scanning method for surface area measurement. Figure 6 The formula for calculating gold quality and the relationship between parameters are shown in the diagram. Detailed Implementation

[0033] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. Unless otherwise specified, the methods used in the embodiments of the present invention are conventional methods, and the reagents used are commercially available.

[0034] Example 1: A non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement This invention provides a non-destructive method for determining the gold mass of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement. The core idea is to measure the thickness of the gold plating layer by utilizing the reflection characteristics of ultrasonic waves at the gold-silver interface, and combine this with the accurate measurement of the sample surface area to obtain the total mass of gold in the jewelry through a mass calculation formula.

[0035] Step 1: Surface cleaning treatment Place the gold-plated silver jewelry to be tested in anhydrous ethanol or a special jewelry cleaning solution for ultrasonic cleaning for 3-5 minutes to remove surface oil, sweat, cosmetic residue, and other substances that may affect ultrasonic coupling. After cleaning, rinse with deionized water and dry for later use.

[0036] Objective: To ensure good coupling between the ultrasonic probe and the sample surface and to eliminate interference from surface contaminants on the measurement signal.

[0037] Step 2: Surface condition inspection Inspect the sample surface under a 10x magnifying glass and rule out the following situations: 1. The surface has obvious scratches, pits, bumps and other defects.

[0038] 2. The coating has quality problems such as peeling, blistering, and exposure of the substrate.

[0039] 3. The surface has non-metallic decorations such as gemstone inlays and enamel (these areas cannot be measured by ultrasound).

[0040] The aforementioned abnormal areas should be marked and excluded in subsequent measurements.

[0041] Step 3: Select the ultrasonic probe frequency Based on the expected thickness range of the gold plating layer to be tested, the probe frequency should be selected according to the following principles: Table 1 .

[0042] Frequency selection principles: 1. The higher the frequency, the better the vertical resolution, but the shallower the penetration depth.

[0043] 2. For thin-layer gold plating, it is recommended to use a high-frequency probe with a frequency of ≥50MHz.

[0044] 3. For thick gold plating (greater than 25μm), a 15-50MHz probe is sufficient.

[0045] Step 4: Select probe type Choose the appropriate probe type based on the sample shape and measurement requirements: 1. Focusing probe: Suitable for flat or gently curved samples, it focuses the sound beam on the region of interest, improving the signal-to-noise ratio of local measurements.

[0046] 2. Delay block probe: A delay block is added between the probe and the sample to extend the near-field length, which is suitable for thin-layer measurement.

[0047] 3. Water immersion probe: The sample is immersed in a water coupling agent, which is suitable for complex shapes or batch measurements and has a good coupling effect.

[0048] 4. Water jet probe: Uses a fine water jet as a coupling agent, suitable for large samples that cannot be completely submerged.

[0049] Step 5: System Calibration The system should be calibrated using a standard reference sample with a known gold layer thickness. The gold layer thickness of the standard sample should cover the expected thickness range of the sample to be tested, and the substrate material should be consistent with that of the sample to be tested (silver or a silver alloy).

[0050] Calibration steps: 1. Place the standard sample at the same measurement position as the sample to be tested.

[0051] 2. Adjust the instrument parameters (gain, gate position, threshold, etc.) to make the displayed thickness consistent with the standard value.

[0052] 3. Verification and calibration: Measure another standard sample of known thickness to confirm that the measurement error is within the allowable range.

[0053] Calibration cycle: Recalibrate after measuring 10 samples, or after changing the measurement location.

[0054] Step 6: Determine the layout of measurement points Develop a measurement point layout plan based on the sample shape and size: 1. Regularly shaped jewelry (such as rings, pendants, simple flat pieces): 1) Prioritize measuring areas with flat surfaces.

[0055] 2) There should be no fewer than 5 measurement points, evenly distributed on the main surface; 3) For symmetrical shapes, only half of the area may be measured, and the measurement may be expanded symmetrically if necessary.

[0056] 2. Jewelry with complex shapes (such as necklaces, bracelets, and openwork jewelry): 1) Divide the sample into several functional areas (such as links, connectors, body, etc.).

[0057] 2) Select 3-5 representative measurement points for each functional area; 3) Record the proportion of each area in the total surface area.

[0058] 3. Measurement point marking: 1) Use a soft marker to lightly mark the measurement points on the sample.

[0059] 2) Alternatively, use a positioning fixture to ensure consistent positioning for each measurement.

[0060] Measurement point selection principles: Prioritize areas with smooth surfaces and normal plating appearance; avoid areas with potentially abnormal thickness, such as edges, bends, and weld points; avoid non-gold-plated areas such as gemstone inlays and enamel decorations; for samples with uneven plating, cover both the thinnest and thickest areas.

[0061] Step 7: Perform multi-point thickness measurement At each measurement point, perform the measurements according to the following steps: 1. Apply an appropriate amount of ultrasonic coupling agent to the surface of the measurement point (professional ultrasonic gel or glycerin is recommended).

[0062] 2. Place the probe vertically at the measurement point and gently press to ensure the coupling agent fully fills the gap between the probe and the sample.

[0063] 3. Observe the ultrasonic echo signal displayed on the instrument to ensure that the signal is clear and stable.

[0064] 4. Read and record the gold layer thickness value at that point.

[0065] 5. Repeat the measurement 3 times at each point and take the average value as the thickness value at that point.

[0066] 6. After each measurement, lift the probe and reapply the coupling agent to ensure measurement independence.

[0067] Echo signal interpretation: In thickness measurement mode, typical ultrasonic echo signals include: 1) Surface echo: the first echo emitted by the probe and reflected by the sample surface; 2) Gold layer bottom surface echo (interface echo): the echo reflected by the ultrasonic wave after passing through the gold layer and reaching the gold-silver interface; 3) Multiple echoes: multiple reflections of the above echoes.

[0068] By measuring the time interval between the surface echo and the echo from the bottom of the gold layer. Based on the longitudinal wave velocity cL(Au) of gold material, the thickness of the gold layer is calculated: .

[0069] Longitudinal wave sound velocity of gold materials =3,240 m / s (at 20°C). If the ambient temperature deviates significantly, it should be corrected according to the temperature coefficient (the temperature coefficient of sound velocity for gold is approximately -0.014% / °C).

[0070] Step 8: Calculate the thickness statistics After completing the measurements at all measurement points, calculate the following statistics: 1. Average thickness d(avg): (i=1 to n). Where d i Let be the thickness value at the i-th measurement point, and n be the total number of valid measurement points.

[0071] 2. Thickness standard deviation sd: (i=1 to n).

[0072] 3. Thickness uniformity coefficient CV (coefficient of variation): .

[0073] The thickness uniformity coefficient reflects the uniformity of the coating.

[0074] Step 9: Select the surface area measurement method Choose an appropriate surface area measurement method based on the complexity of the sample shape: Method A: Geometric measurement and calculation method (applicable to regular shapes) For ornaments with regular geometric shapes (such as rings, cylinders, spheres, planes, etc.), the surface area is calculated by measuring the geometric dimensions and using geometric formulas.

[0075] Step 9A-1: Dimension Measurement Use a digital vernier caliper or a three-dimensional coordinate measuring machine with an accuracy of 0.01 mm to measure the following dimensions: 1) Length, width, and height.

[0076] 2) Diameter, inner diameter, outer diameter; 3) Radius of curvature; 4) Angle (if applicable).

[0077] Step 9A-2: Geometric Surface Area Calculation Calculate the surface area based on the measured dimensions using the following formula: 1. Circular jewelry (such as rings, hoops): , where R 外 Let R be the outer radius. 内 Let be the inner radius and h be the height of the ring section.

[0078] 2. Flat, flat decorative items (such as pendants, brooch bodies): , where L is the length and W is the width.

[0079] If the shape is irregular, measure the longest and widest dimensions, estimate it as a rectangle, and multiply it by the shape correction factor K (usually 0.80-0.95, determined based on how closely the shape resembles a rectangle).

[0080] 3. Spherical or hemispherical ornaments: , , where R is the radius of the sphere and h is the height of the spherical cap.

[0081] 4. Chain jewelry (necklaces, bracelets, etc.): Lay the jewelry flat and measure its total length L and the width of each link w: , where N (factor) is a correction factor (considering factors such as chain link overlap and lateral exposure, usually taken as 1.2-1.5).

[0082] Method B: 3D scanning method (suitable for complex shapes) For jewelry with complex geometric shapes, 3D scanning technology is used to obtain surface area data.

[0083] Step 9B-1: 3D Scanning Use an optical 3D scanner (such as a blue light scanner or a structured light scanner) to scan the jewelry from all angles to obtain 3D point cloud data or STL mesh models of the jewelry.

[0084] Step 9B-2: Model Processing and Area Calculation Import the scanned data into 3D processing software (such as Geomagic, MeshLab, etc.) and perform the following processing: 1) Remove artifacts caused by the support structure; 2) Fill holes caused by scanning blind spots; 3) Generate a complete polygonal mesh model; 4) Calculate the surface area of ​​the mesh model.

[0085] Method C: Drainage method combined with geometric correction (suitable for small, complex ornaments).

[0086] For small, complex ornaments that cannot be 3D scanned, the volume can be measured using the displacement method, and the surface area can be estimated by combining the geometric features.

[0087] Step 9C-1: Measure volume using the displacement method Using an electronic analytical balance with an accuracy of 0.001 mL, the mass m(air) of the ornament in air and the mass m(liquid) immersed in a liquid of known density were measured according to Archimedes' principle. .

[0088] Step 9C-2: Surface Area Estimation For ornaments with relatively regular shapes, the surface area can be estimated in the following ways: 1) Calculate the equivalent size based on the volume and shape characteristics; 2) Calculate the theoretical surface area using the equivalent size; 3) Introduce a shape correction factor based on the surface complexity (the length-width-height ratio obtained by the drainage method).

[0089] Step 10: Determine the overall correction coefficient K The overall correction factor K is used to correct the following systematic biases: 1. Coating porosity correction K p : 1) Micropores may exist in the coating, with porosity typically in the range of 0.1%-2%.

[0090] 2) For decorative gold-plated jewelry, the porosity is generally low (<0.5%).

[0091] Where p is porosity.

[0092] 2. Surface roughness correction K r 1) The actual gold-plated surface is not ideally smooth and has a certain degree of surface roughness; 2) The surface roughness makes the actual surface area larger than the geometric surface area.

[0093] (Approximate estimate), where Ra is the surface arithmetic mean roughness (μm), which can be measured by a roughness tester or determined based on coating process experience.

[0094] 3. Thickness non-uniformity correction K u : To account for the non-uniformity of the coating thickness distribution, K needs to be introduced. u .

[0095] (Approximate estimate), where CV is the thickness variation coefficient.

[0096] 4. Overall correction factor: , Typical range of K values: 1) For high-quality decorative gold-plated jewelry, the K value is usually between 0.98 and 1.02; 2) For gold-plated jewelry with ordinary craftsmanship, the K value may be between 0.95 and 1.05; 3) If necessary, the K value can be determined by actual measurement using a reference sample (a standard sample with known gold quality).

[0097] Step 11: Calculate the gold mass Substitute the parameters determined in the preceding steps into the mass calculation formula: .

[0098] Parameter summary: ρ(Au) = 19.32 g / cm³ 3 (Density of gold at 20°C).

[0099] d(avg): Average thickness of the gold layer (cm), determined by ultrasonic measurement.

[0100] S: Effective surface area of ​​the sample (cm²) 2 ( ), determined by geometric measurement or three-dimensional scanning.

[0101] K: Comprehensive correction coefficient, dimensionless.

[0102] Parameter summary: ρ(Au) = 19.32 g / cm³ 3 (Density of gold at 20°C).

[0103] d(avg): Average thickness of the gold layer (cm), determined by ultrasonic measurement.

[0104] S: Effective surface area of ​​the sample (cm²) 2 ( ), determined by geometric measurement or three-dimensional scanning.

[0105] K: Comprehensive correction coefficient, dimensionless.

[0106] Simplified formula (when thickness is in μm and area is in cm²) 2 When in units): .

[0107] Step 12: Measurement Uncertainty Analysis The uncertainty of the gold quality measurement results is evaluated in accordance with the measurement uncertainty assessment specifications.

[0108] Sources of uncertainty: 1. Uncertainty of thickness measurement u(d): Determined by the measurement accuracy of the ultrasonic thickness gauge, including instrument indication error, repeatability error, environmental influence, etc., and estimated by the standard deviation of multi-point measurement.

[0109] 2. Surface area measurement uncertainty u(S): caused by dimensional measurement error (vernier caliper accuracy: ±0.01mm) and errors introduced by geometric assumptions; for the three-dimensional scanning method: determined by point cloud density and mesh accuracy.

[0110] 3. Uncertainty of density value u(ρ): The density value of gold itself is very accurate (standard value error <0.1%). The main consideration is the effect of temperature: for every 20℃ deviation of temperature, the density changes by about 0.3%.

[0111] 4. Correction coefficient uncertainty u(K): Uncertain estimates of parameters such as porosity and surface roughness.

[0112] Combined uncertainty: Assuming that the uncertainty components are independent, the combined uncertainty is: .

[0113] Expanded uncertainty: Taking a coverage factor k=2 (corresponding to approximately a 95% confidence level), the expanded uncertainty is: .

[0114] Example 2: Determination of Gold Quality in a Regular Circular Gold-Plated Ring 1. Sample Information: The sample to be tested is a gold-plated silver ring with a nominal gold layer weight of 0.14g, a ring size of approximately size 12 (diameter of approximately 20mm), a ring cross-section width of approximately 2.5mm, and a thickness of approximately 1.5mm.

[0115] 2. Sample Preparation: Place the ring in anhydrous ethanol and ultrasonically clean for 5 minutes to remove surface oil. Rinse with deionized water and gently dry with a lint-free cloth. Inspect the surface under a 10x magnifying glass to confirm that the plating is intact and free from defects such as peeling, bubbling, or exposed substrate. The engraving area on the inside of the ring should not affect the measurement on the outside.

[0116] 3. Ultrasonic thickness measurement: 1) Instruments and equipment: Use an ultrasonic thickness gauge with a frequency range of 50-100MHz (thickness resolution 0.1μm), select a focusing probe (probe diameter 3mm), and use professional ultrasonic gel as the coupling agent.

[0117] 2) Measurement steps: 1. Calibration: Calibrate using a silver-based gold-plated standard sheet with a known gold layer thickness of 10 μm, adjusting the instrument parameters to ensure the displayed value matches the standard value. Verify the measurement using another standard sheet (18.5 μm thick), with an error within ±0.5 μm.

[0118] 2. Measurement point layout: Select 6 measurement points evenly on the outer surface of the ring, located on the front (top arc surface of the ring band), left side, and right side of the ring, with adjacent measurement points spaced approximately 60° apart.

[0119] 3. Point-by-point measurement: Repeat the measurement 3 times at each point and record the results: Table 2 .

[0120] 3) Data processing: (1) Average thickness: d(avg) = (15.33 +15.47 + 15.23 + 15.57 + 15.43 + 15.27) / 6= 15.38 μm.

[0121] (2) Standard deviation of thickness: .

[0122] (3) Coefficient of variation of thickness: CV = (0.13 / 15.38)×100%=0.84%.

[0123] 4) Surface area measurement The ring's geometric dimensions were measured using a digital vernier caliper with an accuracy of 0.01 mm. The outer radius Router = 9.95 mm (ring radius + ring cross-sectional width / 2). The inner radius Rinner = 8.32 mm (ring radius - ring cross-sectional width / 2). The ring cross-sectional height h = 2.50 mm. The surface area was calculated using the formula for annular rings: End face area S(end face) = 2 × π × (Router² - Rinner²) = 2 × π × (9.95² - 8.32²) = 2 × π × 29.78 = 187.02 mm2 2 The outer surface area S (outer surface area) = 2π × R_outer × h = 2 × π × 9.95 × 2.50 = 156.69 mm 2 The inner surface area S (inner surface area) = 2π × R_inner × h = 2 × π × 8.32 × 2.50 = 130.62 mm 2 The lateral surface area S(lateral surface) = S(outer lateral surface) + S(inner lateral surface) = 287.31 mm² 2 The total surface area S = S(end face) + S(side face) = 187.02 + 287.31 = 474.33 mm 2 = 4.74cm 2 Considering the potential for uneven thickness at the end face (thinner at the edges), a shape correction factor K (shape) = 0.95 is introduced. The effective area S (effective) = 4.74 × 0.95 = 4.50 cm² 2 .

[0124] 5) Gold quality calculation 1. Determine the correction factor: Porosity correction: Assuming high-quality gold plating, porosity p < 0.2%, Kp = 0.998. Surface roughness correction: Using mirror polishing, roughness Ra < 0.2 μm, Kr = 1 + 0.2 / 5.38 ≈ 1.037. Thickness non-uniformity correction: Ku = 1 + CV 2=1 + 0.0084² ≈ 1.00007. Overall correction factor: .

[0125] 6) Uncertainty assessment Thickness measurement uncertainty: u(d) = 0.053 μm. Relative thickness uncertainty: u(d) / d = 0.053 / 15.38 = 0.0034%. Surface area measurement uncertainty: Dimensional measurement accuracy ±0.01 mm, relative uncertainty approximately u(S) / S ≈ 0.3%. Density uncertainty: u(ρ) / ρ ≈ 0.05% (negligible). Correction coefficient uncertainty: u(K) / K ≈ 3% (mainly from surface roughness estimation). Combined relative uncertainty: Expanded uncertainty (k=2): .

[0126] 7. Measurement Results The gold content of the ring is: m(Au) = 138 ± 8 mg.

[0127] Example 3: Determination of Gold Quality in a Complex Openwork Gold-Plated Pendant 1. Sample Information Sample to be tested: A silver pendant with a hollow design, the main body is in the shape of a hollow petal, and a synthetic gemstone is set in the center (which does not affect the measurement of the main body). The nominal gold layer thickness is ≥10μm.

[0128] 2. Sample preparation Surface cleaning and condition inspection were performed according to the method in Example 1. It was confirmed that the plating on the edges of the petals in the openwork area was intact, and that the gemstone setting prongs were gold-plated but did not affect the main body measurement.

[0129] 3. Ultrasonic thickness measurement Measurement strategy: Divide the pendant into 4 functional areas: Area A: Front of the main petals (5 measurement points). Area B: Back of the main petals (5 measurement points). Area C: Connecting ring (3 measurement points). Area D: Gemstone setting prongs (excluded, cannot be measured).

[0130] Measurement results: Table 3 .

[0131] Regional weighted average thickness: Since the surface area of ​​each region is different, the overall average thickness needs to be calculated by area weighting.

[0132] 4. Surface area measurement Due to the pendant's complex shape, a 3D scanning method was used to measure its surface area. Scanning equipment: Blue light structured light 3D scanner, with an accuracy of 0.02mm.

[0133] Scanning Steps: 1. Fix the pendant on the rotating platform and adjust the scanning parameters. 2. Perform a 360° omnidirectional scan of the pendant to acquire complete point cloud data. 3. Import the scan data into Geomagic software for processing. 4. Generate a complete polygonal mesh model. 5. Calculate the surface area of ​​the model.

[0134] Measurement results: Table 4 .

[0135] Note: Although area D (gemstone setting prongs) cannot be measured ultrasonically, its surface area is still included in the total surface area because the prongs are also plated with gold. The gold quality in this area will be estimated by other means or by referring to the thickness data of area C.

[0136] 5. Gold quality calculation Calculate the weighted average thickness of the region: = (10.42×1.85 +10.28×1.78 + 10.15×0.32) / (1.85+1.78+0.32) = 10.34 μm.

[0137] Estimated thickness of region D: The gem setting prongs are made in the same way as region C (connecting ring) and have similar thicknesses. The reference value is dC = 10.15 μm.

[0138] Calculate the mass of gold: For regions A, B, and C, calculate directly: m(ABC) = 1.932 × 10.34 × 3.95 × 1.04 = 82 mg. For region D: m(D) = 1.932 × 10.15 × 0.89 × 1.04 = 18 mg. Total mass of gold: m(Au) = 82 + 18 = 100 mg.

[0139] 6. Measurement Results The gold content of the pendant is: m(Au) = 100mg.

[0140] Example 4: Measurement and Verification of Gold-Plated Jewelry with Different Thickness Ranges 1. Verification Objective The applicability and accuracy of the method of the present invention to gold-plated jewelry of different thickness levels were verified.

[0141] 2. Verification Sample Four groups of silver standard samples with different gold plating thicknesses were prepared, with the thicknesses as follows: Table 5 .

[0142] Each group contains 3 samples, each in the shape of a cuboid (50mm×10mm×10mm).

[0143] 3. Measurement conditions Table 6 .

[0144] 4. Measurement Results Table 7 .

[0145] 5. Conclusion The verification results show that: 1. The method of this invention can achieve accurate measurements across a wide range of thicknesses. 2. Measurement accuracy is slightly lower (relative deviation 1.4%) for thin coatings, but still acceptable. 3. Measurement accuracy is higher for medium and thick coatings. 4. The ultrasonic method shows significantly better measurement accuracy than the XRF method for thick coatings (>25 μm).

Claims

1. A non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement, characterized in that, Includes the following steps: (1) Sample preparation: Clean the surface of the gold-plated silver jewelry to be tested to remove oil and impurities, check the surface condition and mark abnormal areas; (2) Ultrasonic thickness measurement: Select an ultrasonic probe of appropriate frequency to measure the gold layer thickness at multiple measurement points on the surface of the jewelry, and obtain the thickness value d at each measurement point. i ; (3) Surface area measurement: The effective surface area S of the ornament is measured by geometric measurement method, three-dimensional scanning method or drainage method; (4) Gold mass calculation: Based on the thickness and surface area obtained in steps (2) and (3), the gold mass is calculated according to the following formula after calibration: ； Where ρ(Au) is the density of gold, d(avg) is the average thickness of the gold layer, S is the effective surface area of ​​the jewelry, and K is the comprehensive correction coefficient. (i=1 to n), where n is the total number of valid measurement points; (5) Uncertainty assessment: perform uncertainty analysis on the gold quality measurement results and give the expanded uncertainty of the measurement results.

2. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, In step (2): When the gold plating thickness is 10-25μm, select a probe with a frequency of 100-200MHz; When the gold plating thickness is 25-50μm, select a probe with a frequency of 50-100MHz; When the gold plating thickness is 50-100μm, select a probe with a frequency of 15-50MHz; When the gold plating thickness is greater than 100μm, select a probe with a frequency of 5-15MHz.

3. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, The selection of the ultrasonic probe in step (2) includes any one or a combination of the following: Focusing probe, suitable for measuring samples on flat or gently curved surfaces; Delay block probes are suitable for thin-layer measurements or extending near-field lengths. Water immersion probe, suitable for complex shapes or batch measurements; Water spray probe, suitable for large samples that cannot be completely submerged.

4. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, Step (2) uses the high-frequency pulse echo method to measure the gold layer thickness. The specific steps of the measurement include: S.1 emits ultrasonic pulses onto the gold surface; S.2 Acquire signals from surface echo and gold-silver interface echo; S.3 Measure the time interval Δt between the surface echo and the interface echo; S.4 According to the formula Calculate the gold layer thickness, where =3,240 m / s is the longitudinal wave velocity of the gold material.

5. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, In step (2): For jewelry with a regular shape, at least 5 measurement points should be evenly distributed on the surface; For jewelry with complex shapes, divide the jewelry into several functional areas, and select 3-5 representative measurement points for each functional area.

6. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, The thickness uniformity assessment in step (2) includes the following steps: according to the formula, (i=1 to n) Calculate the standard deviation sd of the thickness at each measurement point, according to the formula. Calculate the coefficient of variation (CV).

7. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, Step (3) uses the geometric measurement method to measure the S of regular-shaped ornaments and the drainage method to measure the S of small, complex ornaments that cannot be 3D scanned. Both the geometric measurement method and the drainage method include the introduction of correction coefficients. The comprehensive correction coefficient K is calculated according to the following formula: ； in: Kp is the coating porosity correction coefficient, Kp=1-p, where p is the porosity; Kr is the surface roughness correction coefficient, K(r)=1+Ra / d(avg), where Ra is the arithmetic mean surface roughness; Ku is the thickness non-uniformity correction coefficient, K(u) = 1 + CV 2 CV is the thickness variation coefficient.

8. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, Step (3) involves measuring the S-shape of the complex-shaped ornament using a three-dimensional scanning method, which includes the following steps: K.1 uses an optical 3D scanner to scan the jewelry from all angles to obtain 3D point cloud data; K.2 imports the scanned data into 3D processing software for processing and mesh generation; K.3 Calculate the surface area of ​​the mesh model.

9. The non-destructive method for determining the gold quality of thick-layer gold-plated silver jewelry based on ultrasonic thickness measurement according to claim 1, characterized in that, The uncertainty assessment in step (5) includes: The thickness measurement uncertainty u(d) is evaluated and estimated using the standard deviation of multi-point measurements; The uncertainty of surface area measurement, u(S), is determined by the accuracy of the dimensional measurement. Evaluate the uncertainty of the correction coefficient u(K); Calculate the combined uncertainty uc; Taking the coverage factor k=2, calculate the expanded uncertainty U(m(Au)); The gold quality determination results are expressed as m(Au)±U(m(Au)).

10. The application of the method according to any one of claims 1-9 in the field of precious metal jewelry testing.

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