A Pt(IV) intermediate, a Pt(IV) phosphate complex aqueous solution, a preparation method, and applications thereof

Abstract

The present invention discloses a Pt(IV) intermediate, a Pt(IV) phosphate complex aqueous solution, a preparation method, and applications thereof. The intermediate is [Pt(NH3)2(OH)4]. A [Pt(NH3)5(OH)]2[HPO4]3 aqueous solution is synthesized using the intermediate as a raw material. The aqueous solution is used as a platinum source to prepare an electroplating solution, and the performance of depositing platinum layers on high-temperature alloys K414 and IC21 is investigated. The results show that, under the existing formula, the Pt(IV) bath solution has good depth capability, uniform and stable coatings; the bonding strength between the platinum coating and the nickel-based alloy substrate is 23.1 MPa, the diffusion layer has excellent oxidation resistance, and the oxidation weight gain rate of the test piece after aluminizing is 0.0075 g / (m 2 h), belongs to the complete antioxidant level, and has excellent high temperature resistance and antioxidant properties.

Description

Technical Field

[0001] The present invention relates to a Pt(IV) intermediate, a Pt(IV) phosphate complex aqueous solution, a preparation method and applications thereof, and particularly to a [Pt(NH3)2(OH)4] intermediate in which hydroxyl and ammonia serve as ligands to coordinate with Pt, a Pt(IV) phosphate complex thereof [Pt(NH3)5(OH)]2[HPO4]3 and a synthesis method thereof, as well as application of the Pt(IV) phosphate complex as a main salt for electroplating on high-temperature alloys. This application has good application prospects in the field of electrochemical platinum plating. Background Art

[0002] The following structural formulas a to g are all possible structures of hydroxyl and ammonia as ligands coordinated with Pt(IV), among which structures a, e and f have been disclosed and confirmed. CN113278034 A, CN114349081A, CN 110156841 A and CN 109795992 A disclose [Pt(NH3)4(OH)2] 2+ 、[Pt(NH3)5(OH)] 3+ 、[Pt(NH3)6] 4+ and [Pt(OH)6] 2- Most of the chemical synthesis methods use K2PtCl4 as raw material and obtain [Pt(NH3)4] through ammonia coordination. 2+ , and then the target complex is obtained through axial oxidation. Due to the high solubility of chlorine in water, it is almost impossible to completely remove the chlorine element.

[0003]

[0004] [Pt(NH3)6] 2+ The optimal synthesis process is direct substitution with ammonia, but due to the coordination effect of Cl, direct substitution of ammonia with chloroplatinic acid can only produce [Pt(NH3)5Cl] 3+ The axial Cl cannot be completely replaced by ammonia, so complete removal of the Cl from chloroplatinic acid is typically achieved by dechlorination with Pt(II), followed by oxidation with Pt(II) to Pt. The structures of b, c, and d are hypothesized to be possible intermediates, but no synthetic process has been reported to isolate and purify the pure products.

[0005] Pt electroplating solutions can be divided into two categories, namely divalent and tetravalent platinum salts. Typical platinum salts are shown in Table 1.

[0006] Table 1. Typical platinum salts

[0007]

[0008] The pH of the plating solution of chloroplatinate and "DNS salt" in acidic baths must be controlled at pH < 2. Hydrolysis will begin when pH > 2. The platinum salts commonly used in alkaline bath electrochemical platinum plating are mainly K2Pt(OH)6, "P salt" and "Q salt". The conductive ion provided by K2Pt(OH)6 is [Pt(OH)6] 2- , ARPowell obtained Brit PAT.363569 in 1913, when C Pt When the current efficiency drops sharply, C Pt When the concentration is >12g / L, the current density is 2.5A / dm 2 The "P salt" process discovered by W. Keitel has a low current efficiency of approximately 10-20%, and ammonia volatilizes quickly, requiring continuous addition of ammonia. Since ammonia is used as the base solution, general metals will be corroded. The biggest disadvantage of the "Q salt" process is the difficulty in adjusting the plating solution. In addition, during operation, Pt(II) is easily oxidized to a yellow, insoluble substance, PtO2·nH2O, which covers the anode surface and forms suspended impurities. The anode needs to be repeatedly removed and wiped to remove the oxide, resulting in a cumbersome process and reducing the utilization rate of platinum. In terms of high-temperature alloy applications, the deposited layer prepared by existing electroplating platinum salts has holes, which affects the density of the coating. In the subsequent oxidation process, internal oxidation is easily formed at the location of the holes, affecting the antioxidant properties of the entire coating. Summary of the Invention

[0009] To this end, the technical problem to be solved by the present invention is to solve the problems of +2-valent platinum salts being oxidized to PtO2·nH2O precipitation and coating the anode in the alkaline electroplating bath. By designing and synthesizing a Pt(IV) phosphate complex, and using the complex as the platinum source and "Q salt" as a reference, it is deposited on a single crystal high-temperature alloy under the proprietary bath solution formula and process, and the performance of the deposited layer is examined.

[0010] The technical solution of the present invention is:

[0011] A Pt(IV) intermediate, wherein the Pt(IV) intermediate is [Pt(NH3)2(OH)4], and its chemical structure is:

[0012]

[0013] A method for preparing a Pt(IV) intermediate, comprising:

[0014] Using Pt(NH3)2I2 as raw material and dilute nitric acid as oxidant, first heat and oxidize I -I2 is used to separate the halogen from the reaction system to obtain the unstable intermediate Pt(NH3)2(OH)2, and then dilute nitric acid is used to continue to oxidize Pt(II) to Pt(IV). Finally, KOH is used to adjust the pH value of the solution to obtain the target complex [Pt(NH3)2(OH)4] precipitation.

[0015] A method for preparing an aqueous solution of a Pt(IV) phosphate complex, wherein the Pt(IV) phosphate complex is [Pt(NH3)5(OH)]2[HPO4]3, and the preparation method comprises:

[0016] [Pt(NH3)2(OH)4] is prepared into a slurry suspension, and ammonium phosphate is added. The mixture is stirred at room temperature and dissolved to obtain an aqueous solution of the target complex [Pt(NH3)5(OH)]2[HPO4]3. The specific process route is as follows:

[0017]

[0018] Furthermore, in the above preparation method, the material molar ratio is [PtCl6] 2- :NO2 - : Ammonium salt = 1:6~10:2~3.

[0019] [Pt(NH3)5(OH)]2[HPO4]3 is used as a platinum source in an electroplating solution; further, the electroplating solution configured with the platinum source is used to electroplate a platinum layer on high-temperature alloys K414 and IC21.

[0020] The synthesis process of a Pt(IV) intermediate and a Pt(IV) phosphate complex of the present invention has the following characteristics:

[0021] (1) Synthesis method of intermediates: Chlorides such as chloroplatinic acid are the raw materials of all basic platinum compounds. Removing the chlorine element therefrom has always been one of the difficulties faced by workers working on platinum group metal compounds. The current solutions are basically implemented through processes such as water washing, silver salt precipitation, ion exchange and semipermeable membranes. Among them, water washing is the most commonly used process in industry, but this method easily produces a large amount of wastewater, and the chlorine therein cannot be completely removed. Bromine and iodine are both halogens with similar chemical properties as chlorine. Br2 and I2 are easy to delaminate and sublime, but Br2 has serious biological damage, which is not conducive to the environment and the safety of related practitioners. For this reason, the present invention uses Pt(NH3)2I2 as raw material and dilute nitric acid as oxidant, first oxidizing I -I2 is then converted to I2, and the easy sublimation of I2 is used to separate the halogen from the reaction system to obtain the unstable intermediate Pt(NH3)2(OH)2. Dilute nitric acid continues to oxidize Pt(II) to Pt(IV), and then the pH of the solution is adjusted to 6-7 with KOH to obtain the target compound [Pt(NH3)2(OH)4] as a yellow precipitate. Its structural characteristics are: [Pt(NH3)2(OH)4] is a neutral complex formed by 2 NH3 and 4 OH coordinated with Pt(IV), and its structural formula is:

[0022]

[0023] (2) Synthesis of [Pt(NH3)5(OH)]2[HPO4]3 aqueous solution: [Pt(NH3)2(OH)4] is prepared into a slurry suspension, and ammonium phosphate is added. The mixture is stirred at room temperature and dissolved to obtain a [Pt(NH3)5(OH)]2[HPO4]3 aqueous solution of the target compound. The specific process route is as follows:

[0024]

[0025] (3) Using Pt(IV) phosphate complex as the platinum source and "Q salt" as the control, the deposited platinum layer obtained after working with the configured bath solution has the following characteristics:

[0026] Under the existing formula, the bath has good depth capability, deposits a uniform and stable platinum layer, and the coating dispersion capability is weaker than that of the coating produced by the "Q salt" bath;

[0027] The bonding strength between the Pt(IV) salt deposited platinum layer and the nickel-based alloy substrate is higher than that of the “Q salt”;

[0028] The high-temperature oxidation resistance of the diffusion layer of IC21 / Pt(IV) is better than that of IC21 / Q;

[0029] The oxidation weight gain rate of IC21 / Pt(IV) aluminized specimen is 0.0075g / (m 2 h), belongs to the complete antioxidant level and has excellent ultra-high temperature antioxidant performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 .Microscopic morphology of platinum surface electroplated in two bath solutions.

[0031] Figure 2 .Appearance before and after bonding strength test.

[0032] Figure 3 .Surface and cross-sectional micromorphology after platinum diffusion coating on IC21 alloy.

[0033] Figure 4Macroscopic appearance of IC21 / Pt diffusion test piece after 1150℃ heat resistance test.

[0034] Figure 5 Oxidation weight gain curve of IC21 / Pt diffusion specimen during 1150℃ / 100h heat resistance test.

[0035] Figure 6 .EDS element distribution diagram of the cross section of IC21 / Pt diffusion specimen.

[0036] Figure 7 .Surface and cross-sectional microstructure of IC21 / PtAl coating.

[0037] Figure 8 Macroscopic appearance of IC21 / PtAl specimen after oxidation resistance test at 1150℃.

[0038] Figure 9 .IC21 / PtAl test piece 1150℃ / 100h oxidation resistance weight gain curve.

[0039] Figure 10 .Technical roadmap for the preparation of the Pt(IV) phosphate complex [Pt(NH3)5(OH)]2[HPO4]3 of the present invention. DETAILED DESCRIPTION

[0040] Example 1. Preparation of a small amount of [Pt(NH3)5(OH)]2(HPO4)3

[0041] Weigh 9.66 g (0.02 mol) of Pt(NH3)2I2, add 200 g (5.56 mol) of distilled water to make a slurry, add 10 mL of concentrated nitric acid, boil until the solution turns dark red, then add 200 g of distilled water to dilute it, heat and boil again to remove most of the acid, cool to room temperature, adjust the pH of the solution to 6-7 with 5% KOH, stir the reaction for 3 h, filter, wash with distilled water 3-4 times, and vacuum dry for 5 h to obtain 5.12 g of [Pt(NH3)2(OH)4] as a yellow powder with a yield of 86.18%.

[0042] Structural data: (1) Chlorine content <3 ppm; (2) Elemental analysis: The measured values ​​of Pt 65.41%, H 3.85%, N 9.36% are consistent with the theoretical values ​​of Pt 65.65%, H 3.36%, N 9.42%, and conform to the elemental composition of [Pt(NH3)2(OH)4]; (3) Easily soluble in dilute acid and alkaline solutions.

[0043] Weigh 2.97 g (0.01 mol) of [Pt(NH3)2(OH)4], add 50 mL of distilled water to make a slurry, add 50 mL of an aqueous solution containing 2.66 g (0.02 mol) of ammonium (NH4)2(HPO4), and stir at 80°C for 5 h. After the solution changes from red to a colorless or light yellow transparent solution, dilute with water to a volume of about 250 mL. The platinum content is detected to be 7.58 g / L, and the yield is 97.17%; the chlorine content is <3 ppm.

[0044] Example 2. Batch preparation of [Pt(NH3)5(OH)]2(HPO4)3

[0045] Weigh 483 g (1 mol) of Pt(NH3)2I2, add 4 kg (222 mol) of distilled water to make a slurry, add 300 mL of concentrated nitric acid, boil until the solution turns dark red, then add 4 kg (222 mol) of distilled water to dilute, heat and boil again to remove most of the acid, cool to room temperature, adjust the pH of the solution to 6-7 with 5% KOH, stir the reaction for 3 h, filter, wash the filter cake with distilled water 3-4 times, and vacuum dry for 5 h to obtain 275.5 g of [Pt(NH3)2(OH)4] as a yellow powder with a yield of 92.76%.

[0046] Structural data: (1) Chlorine content <3 ppm; (2) Elemental analysis: The measured values ​​of Pt 65.41%, H 3.85%, N 9.36% are consistent with the theoretical values ​​of Pt 65.65%, H 3.36%, N 9.42%, and conform to the elemental composition of [Pt(NH3)2(OH)4]; (3) Easily soluble in dilute acid and alkaline solutions.

[0047] Weigh 148.5 g (0.5 mol) of [Pt(NH3)2(OH)4], add 500 mL of distilled water to make a slurry, add 2 L of aqueous solution containing 133 g (1 mol) of ammoniated (NH4)2(HPO4), stir and react at 80°C for 5 h. After the solution color changes from red to colorless or light yellow transparent solution, dilute with water to a volume of about 11.21 L. The platinum content is 8.1 g / L and the yield is 93.12%; the chlorine content is <3 ppm.

[0048] Example 3. Initial solution electroplating ability test

[0049] Taking "Q salt" as a reference, Pt(Ⅳ) salt and "Q salt" bath solutions were prepared respectively according to the existing electroplating bath formula. The two bath solutions were tested using a Hall cell. The cathode used a copper-zinc alloy sheet and the anode used a platinum-plated titanium mesh. The bath solution pH, temperature, Pt concentration, conductive salt, additives, etc. were all the same. The test used a current of 1A, a single electroplating time of 10 minutes, and the pH was alkaline above 10.5.

[0050] Under current density of 3.5 and low current density, the coating of Pt(IV) salt bath is thinner, and there is leakage plating in local areas. The current density coverage ability of Pt(IV) salt bath is lower than that of "Q salt" bath, but it can basically meet the requirements of electroplating production. Both baths have coatings on the back, and both have excellent deep plating ability, but "Q salt" has a larger coating range and stronger deep plating ability. The coating of Pt(IV) salt bath can be seen to be obviously thinned, while "Q salt" bath does not have this phenomenon. Therefore, under the existing formula, the dispersion ability is weaker than that of "Q salt" bath.

[0051] Example 4. Evaluation of coating appearance, area and coating micromorphology

[0052] Using "Q salt" as a reference, a Pt(IV) salt bath and a "Q salt" bath were prepared according to the same existing electroplating bath formula. The platinum salt concentration was 2 g / L in both cases. A platinum layer of ~1 μm was deposited on a nickel-based alloy (K414) measuring 2.5 cm × 2.5 cm × 2 mm. The thickness was measured using an XRF coating thickness gauge. The appearance and area of ​​the coating were tested visually or with the aid of a magnifying glass. The electroplating parameters are shown in Table 1. Results: Both baths were able to electroplate platinum on the K414 alloy. The overall coating exhibited a uniform silver-white color, free of common electroplating defects such as flaking, peeling, ablation, and discoloration.

[0053] Table 1. Electroplating parameters of two baths

[0054] sample Weight gain / g Plating time / min Current / A Voltage / V Coating thickness / μm Q salt 0.0415 25 0.04 1.65 1.2 Pt(IV) salt 0.0489 15 0.06 1.65 1.25

[0055] The coating micromorphology was measured by SEM, with reference to the standard "GB / T 17722 Scanning electron microscope measurement method for thickness of metal cover layer" (such as Figure 1 Results: The surface of the specimen plated with the "Q salt" bath was smoother, while the platinum layer deposited with the Pt(IV) salt exhibited more protruding grains and larger grains. Both coatings were very dense, with no obvious cracks, inclusions, or other defects, save for a small number of micropores. Stable coatings were obtained. Cross-sectional analysis revealed excellent uniformity in both coatings, with no longitudinal cracks observed. Considering that wire-cut electrospark cutting (EDM) during sample preparation could damage the coating, the overall cross-sectional morphology of the coatings was considered normal.

[0056] Example 5. Evaluation of coating bonding strength

[0057] With reference to the standard "GB / T 5210 Paint and varnish pull-off adhesion test", a universal testing machine was used to compare the bonding strength of the coatings prepared by the two bath solutions. K414 nickel-based alloy test piece. Test results are as follows Figure 2As shown, the average bonding strengths of the platinum layers deposited using the two platinum salts were 17.62 MPa and 23.1 MPa, respectively. The three samples (Q-1, Q-4, and Q-5) prepared using the "Q salt" bath exhibited nearly complete peeling during tensile peeling, suggesting a bonding strength of ~20 MPa. In contrast, samples prepared using the Pt(IV) salt bath exhibited complete peeling to a maximum of 35.6 MPa (sample P-5), while the remaining samples exhibited partial peeling. Therefore, the bonding strength of the coatings prepared using the Pt(IV) salt bath to the nickel-based alloy substrate is higher than that of the coatings prepared using the "Q salt" bath.

[0058] Example 6. Evaluation of the heat resistance of the coating and the oxidation resistance of the platinum-aluminum bonding layer

[0059] Taking "Q salt" as a reference, according to the same existing electroplating bath formula, Pt(IV) salt and "Q salt" bath solutions were prepared respectively, and platinum layers of ~3μm were deposited on IC21 nickel-based single crystal high-temperature alloy.

[0060] Vacuum diffusion at 900℃ for 4h forms an interdiffusion layer. Results:

[0061] ① The interdiffusion of the test piece was close to the thickness of the platinum layer. The IC21 / Pt interdiffusion layer of the Pt(IV) salt was thicker than that of the "Q salt" electroplating. The difference was about 6μm, indicating that the density of the platinum layer electroplated by the Pt(IV) salt was weaker than that of the "Q salt" (see Figure 3 );②20~60h, the platinum diffusion test piece prepared by "Q salt" bath solution showed serious deterioration, and then oxide powder was continuously produced. The surface of the test piece was bluish, and the Ni in the alloy was oxidized. However, the platinum diffusion test piece prepared by Pt(IV) salt bath solution still showed gray morphology after 100h oxidation, and no obvious oxide was produced. A relatively stable aluminum oxide and chromium oxide film was formed on the surface of the test piece (see Figure 4 ); ③ Compared with the initial state of the sample, the Pt content in the interdiffusion layer of the two IC21 / Pt platinum diffusion specimens is: IC21 / Pt(IV)>IC21 / Q, and the difference in Pt content can reach 10at% (see Table 2 and Table 3); During high-temperature oxidation, Pt can increase the adhesion between the alumina film and the substrate, and can also prevent the volatilization of refractory solid solution elements such as W and Mo in the alloy, thereby improving the oxidation resistance of the alloy (see Figure 5 ④ Because the Pt content in the Pt diffusion layer of IC21 / Pt(IV) is significantly higher than that of IC21 / Q, the deposited layer of IC21 / Pt(IV) contains more microscopic pores, vacancies, and interface defects than the IC21 / Q group, which increases the interdiffusion rate between the coating and the substrate. Therefore, the Pt diffusion layer of IC21 / Pt(IV) exhibits superior oxidation resistance to IC21 / Q.

[0062] Table 2. EDS element distribution of Pt(Ⅳ) salt bath solution sample group

[0063] area Ni (at.%) Pt (at.%) Al (at.%) Cr (at.%) Co (at.%) 1 43.88 23.51 8.26 12.27 12.08 2 42.01 25.24 10.16 9.17 9.97 3 44.45 26.29 12.90 3.77 5.45

[0064] Table 3. EDS element distribution of Q salt bath sample group

[0065]

[0066]

[0067] 1150℃, place the test piece in a corundum crucible, and test for 100h. Take out the sample regularly for weighing and observation. To ensure the accuracy of the results, each test group contains 3 samples. The results are as follows Figure 6 As shown. Figure 6 It can be seen that the oxidation weight gain rates of IC21 / Q and IC21 / Pt(IV) platinum diffusion test pieces are 0.985 g / (m 2 h) and 0.181 g / (m 2 h), according to HB5258, they all belong to the antioxidant level.

[0068] The IC21 / PtAl coating samples were prepared by Pengzhou Hangda New Materials Co., Ltd. The surface and cross-sectional morphologies of the coatings were characterized by SEM. Figure 7 As shown. Figure 7 It can be seen that the surface grains of the sample group prepared with Pt(IV) salt are larger than those of the sample group prepared with “Q salt”, while the cross sections of the two samples are similar, with no significant differences found.

[0069] The oxidation resistance of the coating was tested according to the standard "HB 5258-2000". The test temperature was 1150℃ and the test time was 100h. Each group of samples consisted of 3 samples. Figure 8 As shown. Figure 8 It can be seen that after undergoing the 1150℃ / 100h test, both samples can maintain the integrity of the surface aluminum oxide film, without the production of oxide scale and local corrosion points, which shows that the high-temperature oxidation resistance of the platinum aluminum coatings prepared by the two platinum salts is similar.

[0070] like Figure 9 As shown in the figure, the oxidation weight gain rate of IC21 / Q and IC21 / Pt(IV) salt platinized aluminized specimens is 0.0056g / (m 2 h) and 0.0075g / (m 2h), according to HB5258, both are fully resistant to oxidation. Their oxidation rates after forming the alumina film are similar, demonstrating excellent ultra-high-temperature oxidation resistance. The main difference is that the Pt(IV) salt group has a lower initial weight gain rate than the "Q salt" group, and the weight gain rate inflection point is lower than that of the "Q salt" group, indicating that the former can more quickly promote the formation of the alumina film, thus protecting the alloy.

Claims

1. A Pt(IV) intermediate, characterized in that: The Pt(IV) intermediate is [Pt(NH3)2(OH)4], and its chemical structure is: 。 2. A method for preparing a Pt(IV) intermediate according to claim 1, characterized in that: Use Pt(NH3)2I2 as the raw material and dilute nitric acid as the oxidant. Boil until the solution turns dark red, dilute with distilled water, and boil again to remove most of the acid. After cooling to room temperature, adjust the pH of the solution with KOH to obtain the target compound [Pt(NH3)2(OH)4] precipitation.

3. The preparation method according to claim 2, wherein: The pH of the adjustment solution is 6-7.

4. The preparation method according to claim 2 or 3, characterized in that: The molar ratio of materials in the preparation is platinum: nitric acid = 1:6~10.

5. A method for preparing an aqueous solution of a phosphoric acid Pt(IV) complex, characterized in that: The Pt(IV) phosphate complex is [Pt(NH3)5(OH)]2[HPO4]3, and its preparation method includes: [Pt(NH3)2(OH)4] prepared by the preparation method according to any one of claims 2 to 4 is adjusted into a slurry suspension, and ammonium phosphate is added. The mixture is stirred at room temperature and coordinated and dissolved to obtain an aqueous solution of the target complex [Pt(NH3)5(OH)]2[HPO4]3.

6. The preparation method according to claim 5, characterized in that: The molar ratio of materials in the preparation is platinum: ammonium salt = 1: 2~3.

7. Use of [Pt(NH3)5(OH)]2[HPO4]3 prepared by the preparation method according to claim 5 or 6 as a platinum source in preparing an electroplating solution.

8. The use according to claim 7, characterized in that The electroplating solution configured with the electroplating platinum source is used in electroplating a platinum layer on a high-temperature alloy.

9. The use according to claim 8, characterized in that The high temperature alloy is K414 or IC21.

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