Anticorrosion properties of copper phosphide

Introduction. – Gülzow: Fachagentur Nachwachsende Rohstoffe e.V., 2010. – 112 p. ANTICORROSION PROPERTIES OF COPPER PHOSPHIDE Abdirakhimov I.E. Karshi state technical university. Abstract. This article presents the results of a study on the anticorrosion properties of copper compounds obtained from spent copper-plating electrolytes. The aim of the work was to develop and test a method for processing waste to produce pigments for protective paint and varnish coatings. Complex metric analysis, X-ray phase analysis, and electrochemical measurements (anodic polarization curves, stationary potential, corrosion current density) were used. It was established that the introduction of pigments based on copper phosphate (Cu₃(PO₄)₂) into coatings provides the lowest corrosion rate and improves electrochemical characteristics compared to control samples. The results confirm the high efficiency of Cu₃(PO₄)₂ as an anticorrosion pigment, opening opportunities for its practical use in industry and rational waste utilization. Keywords: copper phosphide; copper phosphate (Cu₃(PO₄)₂); corrosion resistance; protective coatings; electrochemical methods; electrolyte recycling; anticorrosion pigments. MIS FOSFIDINING KORROZIYAGA QARSHI XOSSALARI Abdiraximov I.E. Qarshi davlat texnika universiteti. Annotatsiya. Maqolada ishlatilgan mis elektrolitlaridan olingan mis birikmalarining korroziyaga qarshi xossalarini oʻrganish natijalari keltirilgan. Ishning maqsadi himoya boʻyoq qoplamalari uchun pigmentlar olgan holda chiqindilarni qayta ishlash usulini ishlab chiqish va sinovdan oʻtkazish . Unda kompleks metrik tahlil, rentgenofaza usuli va elektrokimyoviy oʻlchovlar (anodli polyarizatsiya egri chiziqlari, korroziya tokining zichligi) qoʻllanilgan. Aniqlanishicha, mis fosfat (Cu3(PO4)2) asosidagi pigmentlarni qoplashga kiritish korroziya tezligining eng past qiymatlarini ta’minlaydi va nazorat namunalariga nisbatan elektrokimyoviy xususiyatlarni yaxshilaydi. Olingan natijalar korroziyaga qarshi pigment sifatida Cu3 (PO4)2 ning yuqori samaradorligini tasdiqlaydi, bu esa uni sanoatda amaliy qoʻllash va chiqindilarni oqilona utilizatsiya qilish imkoniyatlarini ochadi. Kalit so‘zlar: mis fosfid; mis fosfat (Cu3(PO4)2); korroziyaga chidamliligi; himoya qoplamalari; elektrokimyoviy usullar; elektrolitlarni qayta ishlash; korroziyaga qarshi pigmentlar. Introduction. Metal corrosion is one of the most pressing problems facing modern industry and society, as the intensive destruction of metal structures leads to significant economic losses. According to international studies, corrosion losses in some countries amount to 3–4% of gross Development of science and technology Scientific and technical journal №1/2026 66 Kimyo va kimyoviy texnologiyalar domestic product [6]. The most significant consequences of corrosion occur in mechanical engineering, energy, transport, marine and aviation industries, pipelines, and construction [1]. In recent еars, scientific and practical directions aimed at reducing the intensity of corrosion have been actively developing. One effective solution is the creation of corrosion-resistant materials, including special stainless steels and phosphorus-containing copper alloys, which exhibit high strength and durability [3]. Another promising approach is the use of new-generation protective coatings. In particular, copper phosphate (Cu₃(PO₄)₂)-based pigments incorporated into paints have shown high efficiency in protecting metal surfaces by forming dense, stable layers that reduce corrosion even in aggressive environments [2]. An environmentally and economically justified approach involves recycling spent copperplating electrolytes. Developed technologies make it possible to extract copper(I) and copper(II) compounds that can be used as pigments for the paint industry [8]. This not only ensures reliable metal protection but also contributes to waste reduction and environmental preservation. Thus, literature analysis and preliminary studies indicate that promising directions for corrosion control include developing new alloys, creating innovative pigments for protective coatings, and using secondary resources rationally. The present study aims to investigate the anticorrosion properties of copper compounds obtained from spent electrolytes and to evaluate their effectiveness in paint coatings. Materials and Methods. Copper (I) and copper (II) compounds used in the study were obtained by a reagent method from spent industrial copper-plating electrolytes from OJSC "Tashkent Tractor Plant". The Cu(II) ion content in electrolyte solutions was determined by complex metric titration with EDTA in the presence of a murex ide indicator [7]. The phase composition of samples was studied using X-ray diffraction on a D8 ADVANCE diffractometer (Germany) within an angle range of 20–80° using SiK radiation [5]. This analysis reliably established the crystalline phases of the obtained compounds. Pigment primers were diluted with solvents to a working viscosity of 18–23 s at 20.0 ± 0.5 °C (by viscometer VZ-246). After filtration, the compositions were applied onto prepared metal plates via pneumatic spraying and dried at 20.0 ± 0.5 °C and 65 ± 5% relative humidity. The coating thickness was measured with a “Konstanta-K5” electromagnetic thickness gauge (AO "Constanta", Russia). Protective and corrosion-resistant properties were studied electrochemically—measuring stationary potential and anodic polarization curves. Measurements were carried out for 24 hours at 20 ± 2 °C using a silver-chloride reference electrode. The potentials were recalculated relative to the standard hydrogen electrode. Anodic polarization curves in 3% NaCl solution were recorded in potentiostatic mode using a PI-50-1 potentiostat and PR-8 controller. The linear parts of the curves were extrapolated to stationary potential to determine the corrosion rate. The corrosion rate was evaluated by mass loss (K) and penetration depth (P) using standard formulas [4]: (1) where Δ m - sample weight loss (g), S - sample surface area (m2), t - test time (h), Δ h - corrosion penetration depth (mm). The use of complex metric, X-ray phase and electrochemical methods together made it possible to carry out reliable identification of the phase composition of pigments and an objective assessment of their protective properties, which justifies the correctness of the chosen methodological approach. “Fan va texnologiyalar taraqqiyoti” Ilmiy-texnikaviy jurnal №1/2026 67 Chemistry and chemical technologies Table 1. Corrosion rates for different pigments As shown in Table 1, pigments based on copper compounds significantly reduce the corrosion rate. The most pronounced protective effect is provided by a copper phosphate pigment (Cu3 (PO4) 2), for which the values of the weight index K and the depth index P are minimal. This confirms the high efficiency of this compound in the composition of primer paints and varnishes. Table 2. Comparison of electrochemical parameters of coatings Sample № Steady-state potential (mV, SHE) Sample № K (mg/( dm2· day)) P (mm/yr) Pigment type 1 12.5 0.12 Control (without pigment) 2 9.8 0.09 Cu (II) phosphate 3 7.6 0.07 Cu (I) oxide 4 5.4 0.05 Cu3(PO4)2 Coating thickness (µм) 1 -420 12.1 42 2 -380 8.7 45 3 -350 6.5 47 4 -310 4.2 50 As shown in Table 2, pigment Cu3(PO4)2 provided the lowest corrosion current density. The results of electrochemical measurements show that the introduction of coppercontaining pigments into the coating composition leads to a positive shift of the stationary potential and a decrease in the density of the corrosion current. At the same time, the thickness of the coating increases, which further enhances its barrier properties. The most favorable electrochemical characteristics are observed in the coating with pigment Cu3(PO4)2, which correlates with the data presented in Table 1. Results and discussions. The compound Cu3(PO4)2, which we need to produce copper phosphide, is reduced by adding carbon to the compound Cu3(PO4)2 Cu3(PO4)2+C+3Cu→2Cu3P+8CO (2) Based on the results of experiments conducted at Tashkent Tractor Plant OJSC, a series of experiments was conducted to study the corrosion resistance of Cu3(PO4)2. According to the results of experiments, among the compounds with the highest copper content, the compound Cu3(PO4)2 was recognized as the most corrosion-resistant, the following results were obtained. The solution is purified by a filter funnel for 4 hours and in an aqueous filtrate it is filtered in 2 minutes. It is possible to determine whether the solution has completely passed through the filter by the appearance of cracks on the filter paper (cracks appear in the completely filtered solution). A colorless solution is formed in the filter, that is, Na2SO4. The copper oxide hydrate cake is dried in an oven at 80 °C for 1 hour. The oven-dried copper oxide dihydrate Cu(OH)2 is separated from the filter paper, ground in a mortar to increase the surface area, and weighed on an analytical balance. 50%concentrated solutions of phosphate chelate and copper oxide dihydrate are prepared. They are heated and mixed in an IKA * LR 1000 base plant at 70 °C for 10 hours in 2 cycles. (These processes are based on reaction 3.2.2 described below.) 3Cu(OH)2+ 2H3PO4→Cu3 (PO4)2+6H2O (3) The pH of the solution was measured with a pH meter for 10 hours. The pH is in the range of 4-5. Cu3 (PO4)2+C+3Cu→2Cu3P+8CO (4) When the indicator of the muffle furnace reaches 1110 °C, the crucible removed from the furnace is poured into a special mold (the mold is coated with fuel oil to evenly distribute the alloy and kaolin to prevent the alloy from adhering to the mold). Then spectral analysis is carried out and Corrosion current (µA/см2) Development of science and technology Scientific and technical journal №1/2026 68 Kimyo va kimyoviy texnologiyalar composition is determined. As a result of the analysis, the alloy contains up to 7.6-8% P, the brand of Cu3P MF9 is obtained. Figure 1 Cu3(PO4)2 over time Figure 2. Copper phosphide alloy, grade Cu3P MF9 According to the results of chemical analysis, the following elements are contained in the 3 copper-containing alloys submitted for testing. Tables 3 and 4 show the composition of copper phosphide alloys. Table 3. Chemical composition of copper phosphide alloys Alloy Cu (%) Zn (%) Fe (%) Sn (%) Sb (%) Pb (%) Al (%) P(%) 1 91.80 0.02 0.17 0.02 0.02 0.003 0.0005 7.62 2 92.30 0.02 0.22 0.02 0.02 0.003 0.0005 7.04 3 91.81 0.02 0.14 0.02 0.02 0.003 0.0005 8.00 “Fan va texnologiyalar taraqqiyoti” Ilmiy-texnikaviy jurnal №1/2026 69 Chemistry and chemical technologies Table 4. Elemental composition of copper phosphide alloy Cu3P № Sample Name Structure Cu Zn Fe Sn Sb Pb Al P 11 Copper (alloy) 91.8 0.02 0.17 0.02 0.02 0.003 0.0005 7.62 22 Copper (alloy) 92.3 0.02 0.22 0.02 0.02 0.003 0.0005 7.04 33 Copper (alloy) 91.81 0.02 0.14 0.02 0.02 0.003 0.0005 8 Figure 3. Dynamics of copper (II) hydroxide formation Figure 3 shows the acceleration of copper hydroxide formation. As can be seen from the graph, the process of formation of copper (II) oxide hydrate occurs unevenly over time, and gradually accelerates. In particular, the sharpest growth is observed between 8 and 10 hours. This indicates that the reaction has entered the active phase and the concentration of the substance is approaching saturation. Figure 4. Anode polarization curves of coatings in 3% NaCl solution: copper (II) 1-acetate; copper (I) 2-oxide; Copper (II) 3-hydroxycarbonate Figure 4 shows the height of the anodic polarization curves of the various pigments. Development of science and technology Scientific and technical journal №1/2026 70 Kimyo va kimyoviy texnologiyalar Table 5. Corrosion resistance of single-layer primer coating Sample Coating thickness δ, mkm Corrosion current i, mkA/cm2 Corrosion level Weight index Km, mg/m2ch Depth index P, mkm/year Cu2O 22-24 1,440 1,5 1,67 Cu(CH3COaO)2 24-25 0,310 0,325 0,364 (CuOH)2CO3 20-22 0,030 0,0318 0,0354 Cu3(PO4)2 21-23 0,018 0,0185 0,0206 steel - 5,623 59,00 65,00 The data in Table 5 show the effectiveness of copper phosphate pigment. Pigments based on copper (II) phosphate are obtained by precipitating copper (II) ions with phosphate ions with preliminary neutralization of acidic copper solutions with a saturated sodium carbonate solution to pH 6. Sodium orthophosphate, saturated sodium hydrogen orthophosphate solutions were used as precipitators, as well as spent chemical degreasing solution (g/dm3): sodium hydroxide NaOH - 6; sodium carbonate Na2CO3-30; sodium orthophosphate Na3PO4 –30. The resulting precipitates were washed by decantation, filtered, dried at 105 °C and crushed. Dried sediments were dense, finely dispersed, sky blue. Based on X-ray phase analysis, the samples were not single-phase and were a mixture of copper (II) phosphates, in which the main phase was copper orthophosphate Cu3(PO4)2. The effect of pigments on the corrosion rate is quantitatively characterized by mass K and depth P, which are presented in the table in comparison with the similar properties of steel in a solution of sodium chloride without a paint coating. For the minimum corrosion current of samples of steel with a single-layer primer coating in sodium chloride solution, the maximum inhibition efficiency was noted for a sample containing copper (II) phosphate, which is a good anode corrosion inhibitor due to its high complexing ability. The mechanism of anticorrosive action of copper (II) phosphate, which is part of the pigment, is the dissociation of phosphate under the influence of moisture penetrating into the paint and the formation of the complex anion [Cu3(PO4)2(OH)2(H2O)2]2, which binds to iron ions in the anode parts, forming stable compounds - complex corrosion inhibitors Fe[Cu3(PO4)2(OH)2(H2O)2]. The protective ability of coatings was evaluated on a ten-point scale by the value of the corrosion depth index. According to the present classification, the coating containing copper (II) orthophosphate obtained from spent copper electrolytes has a resistance score of 4 and belongs to the group of resistant coatings. Conclusion. A method for processing spent copper electrolytes from OJSC "Tashkent Tractor Plant" to obtain copper oxide, acetate, hydroxycarbonate, and orthophosphate has been developed. The synthesized compounds meet the main technical requirements for anticorrosion pigments. Copper phosphate (Cu₃(PO₄)₂) demonstrated the highest efficiency, providing minimal corrosion current values in 3% NaCl solution. Phosphorus-containing copper compounds exhibit strong corrosion resistance and can enhance the durability of metal coatings and alloys. These findings suggest promising prospects for using such compounds in the paint industry and developing advanced protective materials