A method for determining the cobalt and nickel content of a coating
Patent Information
- Application Number
- CN202611128059.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-28
- Publication Date
- 2026-11-03
AI Technical Summary
Existing technologies for detecting cobalt-nickel alloy coatings suffer from high equipment costs, large detection errors, and insufficient stability and repeatability, making them difficult to popularize in small and medium-sized enterprise laboratories.
The contents of cobalt and nickel were determined using a conventional visible spectrophotometer with a pH of 10, a compound system of disodium EDTA, ammonium chloride, and ammonia solution. The pH was adjusted to an alkaline buffer environment. The determination was performed using wavelength-specific detection and interference correction coefficients.
It achieves low-cost and accurate detection of cobalt and nickel content, with a relative standard deviation of ≤2% and a spiked recovery rate of 98% to 102%, making it suitable for batch testing by small and medium-sized laboratories and third-party testing institutions.
Smart Images
Figure CN123029012A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of coating composition analysis technology, specifically to a method for determining the cobalt and nickel content in a coating. Background Technology
[0002] Cobalt-nickel alloy coatings, with their excellent hardness, wear resistance, corrosion resistance, and magnetoelectric properties, are widely used in industries such as electronic components, precision machinery, aerospace, and metal plating. The ratio of cobalt to nickel in the coating directly determines the coating's internal stress, corrosion resistance, deposition rate, and subsequent service life. Therefore, accurately and stably determining the individual contents of cobalt and nickel in cobalt-nickel coatings is a core aspect of electroplating process control, finished product quality inspection, and formula optimization.
[0003] Current conventional detection methods mainly include atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, and traditional chemical titration. The purchase and maintenance costs of large-scale precision instruments are high, making them impractical for small and medium-sized laboratories. Titration is severely affected by coexisting ions, resulting in ambiguous endpoint determination and large detection errors. Conventional spectrophotometry often uses a single, dedicated colorimetric reagent, which is expensive, has a short shelf life, and suffers from insufficient detection stability and repeatability. Summary of the Invention
[0004] 1. The technical problem that the invention aims to solve: This invention provides a method for determining the cobalt and nickel content in a coating, thereby solving the technical problems existing in the background art.
[0005] 2. Technical Solution: To achieve the above objectives, the present invention provides the following technical solution: a method for determining the cobalt and nickel content in a coating, comprising the following steps: A. Pre-treat and weigh the coating sample; B. The coating sample was dissolved by heating with nitric acid to obtain a digestion solution containing cobalt and nickel ions; C. Adjust the volume of the digestion solution to obtain the mother liquor to be tested; D. Prepare a buffer solution with a pH of 8-12 containing disodium EDTA and ammonium chloride; E. Take cobalt and nickel standards, add them to the buffer colorimetric solution described in step D for complexation and color development, and measure the absorbance at the characteristic absorption wavelengths of cobalt and nickel respectively. Establish corresponding cobalt concentration-absorbance standard curves and nickel concentration-absorbance standard curves, and obtain the interference correction coefficients for cobalt and nickel based on the standard curves. F. Take the mother liquor to be tested described in step C, add the buffer colorimetric solution described in step D for complexation colorimetry, and measure the absorbance at the characteristic absorption wavelengths of cobalt and nickel, respectively. G. Based on the absorbance measured in step F and the standard curve and interference correction coefficient described in step E, calculate the concentrations of cobalt and nickel ions in the mother liquor to be tested, and combine the sample weight in step A and the volume determined in step C to obtain the content of cobalt and nickel in the coating.
[0006] Furthermore, in steps E and F, the characteristic absorption wavelength of the cobalt is 490 nm, and the characteristic absorption wavelength of the nickel is 580 nm.
[0007] Furthermore, in step G, the concentration M of cobalt ions in the mother liquor to be tested... CO The concentration M of nickel ions in the mother liquor to be tested NI Calculate using the following formula: ; Among them, A 490 and A 580 These are the absorbance values measured at wavelengths of 490 nm and 580 nm in step F, respectively, where n is the dilution factor, and k1, k2, k3, and k4 are constants determined by the interference correction coefficients. The constants k1 and k2 are used to calculate the cobalt ion concentration, and k3 and k4 are used to calculate the nickel ion concentration.
[0008] Furthermore, interference correction coefficients for cobalt and nickel are obtained based on the standard curve, where k1=68.14, k2=4.8, k3=143.01, and k4=30.71.
[0009] Furthermore, in the buffer colorimetric solution described in step D, the concentration of ammonium chloride is 60-80 g / L, and the concentration of disodium EDTA is 70-90 g / L.
[0010] Furthermore, in step B, the mass concentration of the nitric acid is 65%–68%, the ratio of sample to nitric acid is 1g:20mL, the digestion temperature is 60–80℃, and the digestion time is 15–30min.
[0011] Furthermore, in steps E and F, the settling time for the complexation color development is 10 minutes.
[0012] Furthermore, in step C, the digested solution after being brought to a constant volume is filtered through a 0.45μm microporous membrane to obtain the mother liquor to be tested.
[0013] Furthermore, in step A, the pretreatment includes wiping with anhydrous ethanol to remove oil, rinsing with deionized water, and drying; the drying temperature is 40-60°C, and the drying time is 15-30 minutes.
[0014] 3. Beneficial effects: Compared with the prior art, the technical solution provided by this invention has the following advantages: This invention is rationally designed, employing a compound system of disodium EDTA, ammonium chloride, and ammonia to maintain an alkaline buffer environment at pH 10. All reagents used are common laboratory reagents, widely available, inexpensive, easy to prepare, and have a long shelf life. Maintaining a fixed pH of 10 ensures stable complexation and colorimetric reactions, resulting in good repeatability and a relative standard deviation (RSD) ≤ 2%.
[0015] This invention employs wavelength-specific detection combined with an interference correction coefficient to measure cobalt at 490 nm and nickel at 580 nm, effectively avoiding spectral interference between cobalt and nickel. The spiked recovery rate reaches 98%–102%, with high detection accuracy. Furthermore, it only requires a conventional visible spectrophotometer, eliminating the need for large and expensive equipment such as atomic absorption spectrometers or inductively coupled plasma atomic emission spectrometers. It is easy to operate and suitable for routine batch testing in electroplating plant laboratories and third-party testing institutions, and can be directly applied in industrial applications.
[0016] It should be noted that the structures not described in this invention are not related to the design points and improvement directions of this invention, and are the same as or can be implemented using existing technologies, so they will not be elaborated here. Attached Figure Description
[0017] Figure 1 This is a flowchart of the process flow of the present invention; Figure 2 This is a comparison chart of the measured values and known values of six groups of coating samples with different cobalt-nickel ratios determined by the method of this invention. Detailed Implementation
[0018] To facilitate understanding of the present invention, a more complete description of the invention will be given below with reference to the accompanying drawings. The invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the invention will be more thorough and complete.
[0019] It should be noted that the methods and processes not described in this invention do not involve the design points and improvement directions of this invention, and can all be based on existing technologies known to those skilled in the art.
[0020] Please refer to the attached document. Figure 1-2 The specific implementation of the present invention will be described in detail below with reference to specific embodiments.
[0021] Example 1 This embodiment provides a spectrophotometric detection method for determining the cobalt and nickel content in a cobalt-nickel coating, comprising the following steps.
[0022] Sample pretreatment: Take the cobalt-nickel coating sample to be tested, wipe it with anhydrous ethanol to remove surface oil and oxide deposits, and then rinse it repeatedly with deionized water. Place the cleaned coating sample in a constant temperature oven and dry it at 50℃ for 15 minutes. After taking it out, accurately weigh 0.1g of the coating sample and record the weight for later use.
[0023] Digestion with concentrated nitric acid: Place the weighed coating sample in a 50 mL beaker, add 1.5 mL of 65% concentrated nitric acid (sample mass to concentrated nitric acid volume ratio approximately 1 g : 20 mL), and heat in a fume hood at 70 °C until the coating is completely dissolved. The digestion time is approximately 15 min. After digestion, remove the beaker and allow it to cool naturally to room temperature to obtain a cobalt-nickel mixed digestion solution containing cobalt and nickel ions.
[0024] Preparation of the test stock solution: Transfer the cooled digestion solution to a 50 mL volumetric flask, rinse the inner wall of the beaker repeatedly with deionized water, and transfer the washings to the volumetric flask as well. Add deionized water to the mark and shake well. Filter the diluted digestion solution through a 0.45 μm microporous membrane. The filtrate is the test stock solution, ready for use.
[0025] Preparation of pH=10 buffer solution: Using deionized water as solvent, prepare a mixed solution containing 70 g / L ammonium chloride and 80 g / L disodium EDTA, stirring until fully dissolved. Then, slowly add concentrated ammonia solution dropwise while stirring, and monitor the pH value of the system with a pH meter, adjusting until the pH of the system is stable at 10. Stir the prepared buffer solution thoroughly, let it stand in the dark, and store it for later use.
[0026] Construction of cobalt and nickel standard curves: A gradient series of cobalt and nickel standard solutions with concentrations of 0, 2, 4, 6, 8, and 10 μg / mL were prepared. 5 mL of each gradient standard solution was transferred to a series of colorimetric tubes, and 5 mL of the aforementioned pH=10 buffer solution was added to each. The tubes were shaken well and allowed to stand at room temperature for 10 min for complexation and color development. The absorbance of each cobalt standard solution was measured at 490 nm using a visible spectrophotometer. A cobalt standard curve was plotted with cobalt concentration on the x-axis and absorbance on the y-axis. The correlation coefficient of the obtained cobalt standard curve was ≥0.999. Similarly, the absorbance of each nickel standard solution was measured at 580 nm. A nickel standard curve was plotted with nickel concentration on the x-axis and absorbance on the y-axis. The correlation coefficient of the obtained nickel standard curve was also ≥0.999.
[0027] Based on the Lambert-Beer law, the total absorbance of a mixed component at a certain wavelength is equal to the sum of the absorbances of each component at that wavelength. Using the slopes of the cobalt and nickel standard curves, the absorbance coefficients were obtained. These absorbance coefficients were then substituted into the dual-wavelength interference correction equations to obtain interference correction coefficients k1=68.14, k2=4.8, k3=143.01, and k4=30.71, which were used for subsequent sample content calculations.
[0028] Sample color development and absorbance determination: Transfer 5 mL of the stock solution to a colorimetric tube, add 5 mL of pH=10 buffer solution (the same ratio used for standard curve plotting), shake well, and allow to stand at room temperature for 10 min under the same conditions as for standard curve plotting to develop color and complex. Use a visible spectrophotometer to measure the absorbance of the sample solution at wavelengths of 490 nm and 580 nm, respectively, and record them as A. 490 and A 580 .
[0029] Content calculation: Calculate the content by measuring the sample absorbance A. 490 and A 580 Substitute the values of cobalt ions and nickel ions into the following formula to calculate the concentrations: ; Among them, A 490 and A 580 The absorbance values of the sample solution measured at wavelengths of 490 nm and 580 nm are respectively. In this embodiment, n=2, which is the dilution factor of the mother liquor to be tested (in this embodiment, the digestion solution is brought to a final volume of 50 mL, and 5 mL of the mother liquor to be tested is transferred to 5 mL of buffer colorimetric solution, which is equivalent to a 2-fold dilution); M=mass concentration, in g / L; after calculating the concentrations of cobalt ions and nickel ions in the mother liquor to be tested according to the above formula, and combining the final volume of 50 mL and the sample weight of 0.1 g, the mass percentage of cobalt and nickel in the cobalt-nickel coating can be obtained.
[0030] Example 2 The difference between this embodiment and Example 1 lies in the drying conditions of the sample pretreatment step. The cobalt-nickel coating sample to be tested was wiped clean with anhydrous ethanol to remove oil, rinsed with deionized water, and then placed in a constant temperature oven at 40°C for 20 minutes. The remaining steps and conditions were the same as in Example 1.
[0031] Example 3 The difference between this embodiment and Example 1 lies in the drying conditions of the sample pretreatment step. The cobalt-nickel coating sample to be tested was wiped clean with anhydrous ethanol to remove oil, rinsed with deionized water, and then placed in a constant temperature oven at 60°C for 15 minutes. The remaining steps and conditions were the same as in Example 1.
[0032] Example 4 The difference between this embodiment and Example 1 lies in the digestion time of the concentrated nitric acid heating digestion step. The weighed coating sample is placed in a beaker, and 65% concentrated nitric acid is added. The sample is heated at 70°C in a fume hood until the coating is completely dissolved. The digestion time is 30 minutes. The remaining steps and conditions are the same as in Example 1.
[0033] Example 5 The difference between this embodiment and Example 1 is that the test stock solution was not filtered during preparation. The cooled digestion solution was transferred to a 50 mL volumetric flask, diluted to the mark with deionized water, and shaken thoroughly before being used directly as the test stock solution without filtration through a 0.45 μm microporous membrane. The remaining steps and conditions were the same as in Example 1.
[0034] Effect verification To verify the accuracy and reliability of the method of the present invention, the inventors conducted the following spike recovery test and precision test.
[0035] In cobalt-nickel plating samples with known cobalt and nickel contents, known amounts of cobalt standard solution and nickel standard solution were added, respectively. Pretreatment, digestion, color development, and determination were performed according to the method in Example 1, and the spiked recovery rate was calculated. The results showed that the spiked recovery rate of the method of the present invention was 98%–102%, indicating that the method has high accuracy and can meet the requirements for plating composition analysis.
[0036] like Figure 2 As shown, the method of the present invention was used to measure six groups of coating samples with different cobalt-nickel ratios. The maximum deviation between the measured values and the known values was 0.4 percentage points, and the average deviation was 0.25 percentage points. Moreover, the sum of the measured values of cobalt and nickel in each sample was 100% (±0.1%), indicating that the method of the present invention has high accuracy and can meet the detection requirements of cobalt and nickel content in actual coating samples.
[0037] Meanwhile, the same cobalt-nickel coating sample was measured six times in parallel according to the method in Example 1, and the relative standard deviation (RSD) of the measurement results was calculated. The results show that the relative standard deviation of cobalt and nickel measured by the method of the present invention is ≤2%, further demonstrating that the method has good repeatability and high precision.
[0038] Cobalt single-standard solution, nickel single-standard solution, and cobalt-nickel mixed standard solution were prepared separately. After color development according to the method in Example 1, the absorbance was measured at wavelengths of 490 nm and 580 nm, respectively. The results showed that at a wavelength of 490 nm, cobalt ions had a good absorbance response, while the interference from nickel ions could be effectively subtracted by the correction coefficient in the formula; at a wavelength of 580 nm, nickel ions had a good absorbance response, and the interference from cobalt ions could also be effectively subtracted by the correction coefficient in the formula. This indicates that the wavelength-specific detection combined with the interference correction coefficient scheme adopted in this invention can effectively avoid mutual spectral interference between cobalt and nickel, and has good selectivity.
[0039] The above-described embodiments are merely illustrative of certain implementations of the present invention, and are described in a relatively specific and detailed manner. However, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.
Claims
1. A method for determining the cobalt-nickel content in a coating, characterized in that: Includes the following steps A. Pre-treat and weigh the coating sample; B. The coating sample was dissolved by heating with nitric acid to obtain a digestion solution containing cobalt and nickel ions; C. Adjust the volume of the digestion solution to obtain the mother liquor to be tested; D. Prepare a buffer solution with a pH of 8-12 containing disodium EDTA and ammonium chloride; E. Take cobalt and nickel standards, add them to the buffer colorimetric solution described in step D for complexation and color development, and measure the absorbance at the characteristic absorption wavelengths of cobalt and nickel respectively. Establish corresponding cobalt concentration-absorbance standard curves and nickel concentration-absorbance standard curves, and obtain the interference correction coefficients for cobalt and nickel based on the standard curves. F. Take the mother liquor to be tested described in step C, add the buffer colorimetric solution described in step D for complexation colorimetry, and measure the absorbance at the characteristic absorption wavelengths of cobalt and nickel, respectively. G. Based on the absorbance measured in step F and the standard curve and interference correction coefficient described in step E, calculate the concentrations of cobalt and nickel ions in the mother liquor to be tested, and combine the sample weight in step A and the volume determined in step C to obtain the content of cobalt and nickel in the coating.
2. The method for determining the cobalt and nickel content in a coating according to claim 1, characterized in that: In steps E and F, the characteristic absorption wavelength of the cobalt is 490 nm, and the characteristic absorption wavelength of the nickel is 580 nm.
3. The method for determining the cobalt and nickel content in a coating according to claim 1, characterized in that: In step G, the concentration M of cobalt ions in the mother liquor to be tested CO The concentration M of nickel ions in the mother liquor to be tested NI Calculate using the following formula: ； Among them, A 490 and A 580 These are the absorbance values measured at wavelengths of 490 nm and 580 nm in step F, respectively, where n is the dilution factor, and k1, k2, k3, and k4 are constants determined by the interference correction coefficients. The constants k1 and k2 are used to calculate the cobalt ion concentration, and k3 and k4 are used to calculate the nickel ion concentration.
4. The method for determining the cobalt and nickel content in a coating according to claim 3, characterized in that: The interference correction coefficients for cobalt and nickel were obtained from the standard curve, where k1=68.14, k2=4.8, k3=143.01, and k4=30.
71.
5. The method for determining the cobalt and nickel content in a coating according to claim 1, characterized in that: In step D, the concentration of ammonium chloride in the buffer colorimetric solution is 60-80 g / L, and the concentration of disodium EDTA is 70-90 g / L.
6. The method for determining the cobalt-nickel content in a coating according to claim 1, characterized in that: In step B, the mass concentration of nitric acid is 65%–68%, the ratio of sample to nitric acid is 1g:20mL, the digestion temperature is 60–80℃, and the digestion time is 15–30min.
7. The method for determining the cobalt and nickel content in a coating according to claim 1, characterized in that: In steps E and F, the settling time for the complexation color development is 10 minutes.
8. The method for determining the cobalt-nickel content in a coating according to claim 1, characterized in that: In step C, the digestion solution after being brought to a constant volume is filtered through a 0.45μm microporous membrane to obtain the mother liquor to be tested.
9. The method for determining the cobalt-nickel content in a coating according to claim 1, characterized in that: In step A, the pretreatment includes wiping with anhydrous ethanol to remove oil, rinsing with deionized water, and drying; the drying temperature is 40-60℃, and the drying time is 15-30 min.