Dezincification Process Research Articles

Release of lead, copper, zinc from the initial corrosion of brass water meter in drinking water: Influences of solution composition and electrochemical characterization

Corrosion of brass plumbing materials may lead to metal release and deteriorate the drinking water quality. In this study, the initial corrosion of brass coupon cut from commercially available water meter was investigated. High rates of Pb, Cu and Zn release from the brass coupon were found during the early stage of corrosion (0–5 d) due to general corrosion and galvanic corrosion. The corrosion current density (Icorr) increased and resistance (RF) decreased during this period indicating that severe corrosion had occurred. In a later stage (5–30 d), a decreased Icorr and an increased RF were observed due to the development of a denser layer of Pb and Cu corrosion products which regulated the release of soluble Pb and Cu. The release of Zn continued and no significant Zn precipitation was found. Overall, particulate Pb, particulate Cu and soluble Zn dominated in the metal release during the initial corrosion of brass. The release of Pb, Cu and Zn was enhanced by a lower pH. Free chlorine was found to slightly reduce the release of Pb but promote the release of Cu and Zn. The presence of Pb on the brass surfaces was found to alleviate the dezincification process. A conceptual model based on metal release profile and electrochemical characterization was proposed to describe the initial corrosion of brass in typical drinking water.

Waste control by waste: Extraction of valuable metals from mixed metallurgical dust by boiling furnace roasting

Electric arc furnace dust (EAFD) is a hazardous waste by-product generated during the process of electric furnace steelmaking, which is rich in valuable metal elements. In order to solve the problem of environmental pollution and resource utilization of EAFD, we propose a new process for medium-temperature suspension roasting EAFD and coke dry quenching dust to extract valuable metals. The thermodynamic properties and migration behavior of valuable elements involved in the reaction were analyzed using thermodynamic simulation software FactSage8.1 and thermogravimetric mass spectrometry. The mechanism and kinetic equation of the dezincification process were investigated using the Kissinger method and Coats-Redfern model. The impact of various parameters on the process efficacy and ash fusion characteristics of the material were investigated through boiling furnace experiments. The results demonstrate that elevating the reaction temperature and decreasing the zinc partial pressure is more favorable for reducing and separating zinc. The corresponding kinetic equations for the decomposition of ZnFe2O4 and reduction of ZnO are denoted as dα/dT = 1.69 × 1012exp (−3.37 × 104/T) and dα/dT = 6.76 × 106 exp (−2.08 × 104/T) × (1 − α) [−ln(1 − α)]3/4, respectively. The optimum reaction temperature was 1050 °C, the C/O ratio was 0.8, the reaction time was 40 min, and the ventilation rate was 3500 mL/min. Under these conditions, the material had no liquid phase agglomeration, and the removal rates of zinc and lead were 93.38 % and 98.14 %, respectively. The crude zinc dust with a zinc grade of 87.57 % and the alloy slag with an iron grade of 52.38 % was obtained. The new process utilizes the excellent heat transfer characteristics and fluidization conditions of the boiling furnace to efficiently realize the high-grade recovery of valuable metals in the EAFD, which provides new insights for the clean treatment of zinc-containing waste.

Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins

This study investigated the micro and nanoscale structure in Cu-Zn alloy, as well as its corrosion patterns. To achieve this goal, a set of Roman orichalcum coins were analysed using Scanning Electron Microscopy (SEM-EDS), X-ray maps, high resolution field emission scanning electron microscopy (HR-FESEM-EDS) and electron microprobe analyser (EMPA) techniques. The samples showed a high degree of corrosion on their external surfaces, which evolved in depth up to ~1 mm. Micro and sub-micro imaging of the inner metal highlighted the presence of “stressed areas” caused by mechanical processing work, representing the trigger zone of corrosion and causing the loss of material. These images also permitted us to follow the grain-grain interface and selective Zn-dealloying in the examined samples. X-ray maps of Cu and Zn helped us to understand the evolution of the dezincification process, from rim to core. HR-FESEM-EDS imaging investigation highlighted a heterogeneous composition within the strain line structures, confirming that the mechanically stressed areas were active zones for corrosion processes. Cracks and voids also characterised the patina. Conversely, the uncorroded cores of the samples were not affected by dealloying.

Multi-analytical approach for an archaeometric study on orichalcum coins

Orichalcum is a Cu-Zn based alloy known since the 1st millennium BC. The cementation was the ancient technique used for its production. The PhD project here presented aimed to characterise this alloy and to evaluate its degradation: for this purpose, non-destructive, nano-invasive and destructive techniques were used on a collection of ancient coins issued from the 1st century BC to the end of the 1st century AD. In particular, a multi-analytical approach was used: to investigate the patinas and their corrosive patterns, to study the alloy microstructures and their degradation, to describe the dezincification process and grouping the coins by emission. In addition, quantitative analyses allowed a complete characterization of this ancient alloy. The multi-analytical approach allowed to review the previous theories used for dating samples in orichalcum. This project wanted to contribute to the current knowledge on Roman coinage and to attempt to investigate the mechanisms of corrosive processes affecting ancient alloys.

Croton lechleri Extracts as Green Corrosion Inhibitors of Admiralty Brass in Hydrochloric Acid.

Croton lechleri, commonly known as Dragon’s blood, is a tree cultivated in the northwest Amazon rainforest of Ecuador and Peru. This tree produces a deep red latex which is composed of different natural products such as phenolic compounds, alkaloids, and others. The chemical structures of these natural products found in C. lechleri latex are promising corrosion inhibitors of admiralty brass (AB), due to the number of heteroatoms and π structures. In this work, three different extracts of C. lechleri latex were obtained, characterized phytochemically, and employed as novel green corrosion inhibitors of AB. The corrosion inhibition efficiency (IE%) was determined in an aqueous 0.5 M HCl solution by potentiodynamic polarization (Tafel plots) and electrochemical impedance spectroscopy, measuring current density and charge transfer resistance, respectively. In addition, surface characterization of AB was performed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques. Chloroform alkaloid-rich extracts resulted in IE% of 57% at 50 ppm, attributed to the formation of a layer of organic compounds on the AB surface that hindered the dezincification process. The formulation of corrosion inhibitors from C. lechleri latex allows for the valorization of non-edible natural sources and the diversification of the offer of green corrosion inhibitors for the chemical treatment of heat exchangers.

Corrosion mechanism of CuZn21Si3P in aggressive tap water

Exposure tests of CuZn21Si3P in drinking water and dezincification test solution have revealed good dezincification resistance of the lead‐free brass CuZn21Si3P. To clarify the underlying mechanism, electrochemical measurements in tap water and surface characterisation of samples exposed to drinking water were performed. Open circuit potential measurements, electrochemical impedance spectroscopy and micro‐electrochemical polarisation curves, as well as light‐microscopy, X‐ray diffraction and Auger electron spectroscopy measurements reveal details on the corrosion behaviour and scale formation. Microstructural effects, electrochemical behaviour of the separate phases, and the role of the alloyed phosphorous in the dezincification process could be elucidated. Conclusively, a corrosion mechanism is proposed, that unites and explains the findings of long‐term exposure.

Dissolution Kinetics of α,β′-Brass in Basic NaNO3 Solutions

Corrosion tests at a constant anodic potential, referred to as dissolution tests, were performed to determine the dissolution kinetics of an α,β′-brass CuZn40Pb2 (CW617N) in a basic nitrate solution with and without mechanical loading. The corrosion behavior of the α,β′-brass was characterized by a two-step mechanism, with an initiation step for which the simultaneous dissolution of all the alloying elements of the β′ phase occurred only and a propagation step including at first, the afore-mentioned simultaneous dissolution process before a critical time tc and then, both simultaneous dissolution and dezincification of the β′ phase after tc. The pH and Cu concentration of the electrolyte near the brass surface were determined to be two of the major factors influencing the occurrence of the dezincification process. The dezincification of the β′ phase extended in depth by a percolation dissolution mechanism. Mechanical loading during the dissolution tests was observed to largely influence the dezincification process. It was assumed to open or close the pores present in the dezincified β′ phase, which promoted or slowed down the dezincification mechanism depending on the sign of the stress.

Nanoporous Ag template from partially sintered Ag-Zn compact by dezincification

A novel approach is followed to successfully fabricate nanoporous thin Ag template using partial sintering of elemental Ag and Zn (both have 99.9% purity) and subsequent dezincification. The starting materials for dezincification are partially sintered Ag-Zn aggregates (2.5, 5 and 10 wt% Zn). Partial sintering is done in order to achieve only interfacial bonding with the aim to maintain maximum potential difference between Ag and Zn particles during dezincification process in 1 N HCl and 3.5 wt% NaCl solutions. Two different dissolution methods, namely, simple immersion for 45 days and electrochemical way (holding the sample at critical potential), are employed. Electrochemical polarization tests are carried out to determine the critical potential for subsequent chrono-amperometry. X-ray diffraction, optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy are carried out to examine microstructural evolution, size, distribution and nature of pores in sintered aggregate as well as in template.

Porous copper template from partially spark plasma-sintered Cu-Zn aggregate via dezincification

Present work deals with the preparation of spark plasma-sintered Cu-Zn aggregate (5, 10 and 20 wt% Zn) with interfacial bonding only starting from elemental powders of Cu and Zn (99.9% purity) and subsequently making of porous template of Cu by dezincification. Sintering is done so as to achieve only interfacial bonding with the aim to maintain maximum potential difference between the Cu and Zn particles during dezincification process in various solutions, viz. 1 N HCl and 3.5 wt% NaCl solutions. X-ray diffraction, optical microscopy and SEM-EDS are carried out to examine microstructural evolution and subsequent changes in hardness with sintering temperatures and different Zn percentages. Dezincification and pore formation are conducted on sintered 0.5 mm thick 12 mm diameter disc samples. The size, distribution and nature of pores in porous templates of Cu are then investigated using optical microscopy and SEM-EDS analysis.

Surface and interface investigation of electrochemically induced corrosion on a quaternary bronze

A quaternary (Cu‐Zn‐Sn‐Pb) cast bronze was submitted to an electrochemical corrosion experiment using an anodic polarization sweep. The surface/interface chemical analysis of the patina removed after the anodic polarization and the metallographic observations on the corroded bulk alloy highlight the onset of a dezincification process followed by a decuprification process, as well as the formation of a Sn‐enriched layer located at the interface patina‐bulk alloy. Different local corrosion patterns, as CuCl precipitation in pits, epitaxial growth of corrosion products on dendritic structures and of Cl‐enriched oxyhydroxides, are observed too. The results are discussed in comparison with experimental findings obtained in previous ageing tests performed on the same alloy in different chloride‐containing solutions. Copyright © 2014 John Wiley & Sons, Ltd.

Influence of heat treatment on microstructure and passivity of Cu–30Zn–1Sn alloy in buffer solution containing chloride ions

Tin as an alloying element is of great interest in brasses for dezincification impediment. In this paper, Cu–30Zn–1Sn alloy was submitted to three different heat treatments, viz. A (heating up to 800 °C for 20 h, held at 200 °C for 20 h in salt bath and air cooled), B (heating up to 800 °C for 20 h and water quenched) and C (heating up to 600 °C for 20 h and water quenched). The influence of heat treatment on microstructure was evaluated by OM and SEM–EDS analysis. The corrosion resistance in buffer solution (pH 9), H3BO3/Na2B4O7 ·10H2O, with various concentrations of chloride ions was evaluated by potentiodynamic polarization curves and compared with multi-component Pourbaix diagrams. A correlation between the heat treatment, microstructure and passivity of the heat treated samples was observed. The results indicated that all heat treatment procedures led to formation of α, and γ-Sn-rich phases as microstructure constituents with a small fraction of β′ phase in A. Sn-rich phase appears in grain boundaries and its morphology was slightly changed due to heat treatment. Beneficial influence of low concentration chloride ions on passivity was associated with the formation of copper oxides/hydroxide and chloride complexes. Deterioration was observed at concentrations higher than 0·05 M NaCl due to accelerated dissolution of copper by formation of CuCl\(_{2}^{-}\). As a result of dezincification process, preferential corrosion attack and copper redeposition on α phase (matrix) were observed. However, Sn-rich (γ1) phase in grain boundaries was not attacked due to SnO2 formation. In buffer solution, the higher passivity current density in A was related to the presence of small amount of β′ phase. On the other hand, in 1 M NaCl, lower critical current density for passivation in B and A (about two times lower than C) was attributed to the grain size effect.

Primordial hexagonal phase formation during the bcc dezincification of the β Cu–Zn single crystalline surface: Matrix instabilization and transformation path

Subjecting Cu–Zn samples to annealing under dynamical vacuum produces the evaporation of Zn, a process known as dezincification. Here, we study the phase transitions related to dezincification of Cu–48 at.% Zn (bcc, Beta phase) single crystalline surfaces with residual stresses due to mechanical polishing. In order to identify different steps in the dezincification process of these deformed samples we apply a combination of in situ optical microscopy and transmission electron microscopy (TEM) observations. The former allows us to control and stop the dezincification process at a specific stage of evolution while the latter allows relating surface features with structure and composition changes. Due to dezincification, the formation of an on average 4H hexagonal phase and the fcc equilibrium phase take place. TEM observations show that the bcc to 4H phase transformation occurs by a mechanism of nucleation and growth. In particular, we show evidence of the mechanism of embryo formation for the first time. During the subsequent growth process, the coalescence of transformed zones defines regions in the micron range which after subsequent prolonged dezincification transform to the final fcc equilibrium structure. These experiments provide an insight on the reason for the formation of the non-equilibrium hexagonal phase during the dezincification of electropolished (non-deformed) samples. The new experimental results evidence the heterogeneous character of the dezincification.

Effect of Zn and Pb contents on the electrochemical behavior of brass alloys in chloride-free neutral sulfate solutions

Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of brass alloys with various Zn contents (5.5–38.0 mass%) and Cu–38.0Zn–Pb alloy with different Pb contents (1.0–3.4 mass%) in neutral sodium sulfate solutions. The influence of working conditions, e.g., immersion time, sulfate ions concentration and temperature on the electrochemical behavior of the different alloys was also studied. It was found that the initial corrosion rate is relatively high for alloys with the higher zinc content due to dezincification. The dezincification process initiates by selective dissolution of zinc and continues by a simultaneous dissolution of copper and zinc followed by re-deposition of copper. An increase in the lead content and immersion time in the sodium sulfate solution increases the corrosion resistance of the alloy and improves its stability. The stability of the leaded brass was considered to be due to the formation of an insoluble film of lead sulfate on its surface. The impedance data were fitted to theoretical data obtained according to an equivalent circuit model describing the electrode/electrolyte interface. The mechanism of the alloy dissolution was discussed in view of the obtained results.

Corrosion of cold-deformed brass in acid sulphate solution

The corrosion behaviour and the dezincification process of cold-deformed CuZn-42 brass were tested in an acid sulphate solution at pH-value 2 with additional chloride and copper(II) ions by use of the linear polarization method. The measured corrosion potential and densities of corrosion currents were observed as characteristics of the dezincification process and the corrosion resistance of tested samples of cold-deformed CuZn-42 brass. The results obtained have shown that pH-value 2 of the tested solutions and increased concentrations of copper(II) ions result in increased values of densities of corrosion currents of the tested brass samples, as a result of selective zinc dissolution and the individual dissolution of zinc and copper including the process of anodic oxidation. The tested concentrations of chloride ions in certain conditions have an inhibiting effect, whereas in the other conditions they act as distinctive activators of brass corrosion. The lowest values of corrosion currents are present in the brass samples with the highest deformation degree at 80%. The process of dezincification and anode dissolution of cold deformed brass samples were developed in the whole range of tested potentials.

Dezincification of Brass and its Control - An Overview

The increasing utilization of sea water as a medium for transportation, communication, energy generation, oil and mineral exploitation and as an industrial fluid has direct impact on problems associated with the maintenance of marine structures and machinery. Keeping this in mind, numerous investigations on the corrosion behaviour of various metals and their alloys in natural sea water, fresh water, and acid environments have been carried out. The present review deals with the physical and mechanical properties of brass, binary phase diagram of brass, potential pH diagram of brass, types of dezincification and mechanism of dezincification. In recent years, there has been an enormous growth of industries like chemical, electrochemical, etc., near coastal areas. Therefore, this review also looks at the effect of various pollutants on the dezincification process. Investigations on the control of dezincification of brass in various environments like acid, neutral and in the presence of pollutants are also discussed in derail. Finally, the effect of the addition of alloying elements on the reduction of the dezincification process are explained in detail.

Electrochemical Impedance Spectroscopic Investigations of the Corrosion Behaviour of Brass Alloys in Aqueous Solutions

Brass alloys are technologically important materials due to the wide range of their industrial applications. Extensive efforts have been directed to investigate the corrosion and stability of these alloys. The corrosion behaviour ofthese materials is always related to the study of the dezincification process or the selective dissolution of the active components of the alloy in the different media under different conditions. Due to the lack of systematic study of the electrochemical behaviour of these alloys in aqueous solutions at different pH, it was found essential to cover this area Electrochemical impedance spectroscopy (EIS) and polarization techniques, are powerful to investigate the electrochemical processes occuring at the electrode / electrolyte interface. The techniques enables mechanistic studies beside corrosion rate determination. In this work, the corrosion and passivation behaviours of three different brass alloys in aqueous solutions of various pH, covering the acidic, neutral and basic media were studied and a comparison with the corrosion behaviour of the pure elements under the same conditions made. EIS and polarization techniques beside open circuit potential measurements were used. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were employed to explain and to confirm the corrosion phenomena occuring at the alloy surface. Preliminary data have shown that the selective dissolution of Zn and Pb from the alloys under open circuit conditions occur in acidic and basic media more than in neutral solutions and the behaviour cannot be explained on the basis of pure pH effects.

Electrochemical and spectroscopic studies on dezincification of α-brass: Part II. Effect of polarization on the dezincification process

The phenomenon of dezincification of α-brass in 4% NACl solution (synthetic sea water) following polarization at various potentials was studied using XPS and AES surface analytical techniques. The electrolyte was simultaneously analyzed by atomic absorption. At potentials more negative than the steady state open-circuit potential (E st) of brass, dissolution of both copper and zinc was restricted by the values of the solubilities of Cu 2O and ZnO. At potentials more positive than E st dissolution of α-brass occurred with 100% current efficiency with a rate two orders of magnitude higher than that measured at negative potentials. XPS analysis of the alloy surface following polarization proved the formation of CuCl and two forms of ZnO. Dissolution of copper is assumed to occur through CuCl 2 - where that of zinc is suspected to occur through HZnO 2. The two metals go into solution in a ratio comparable to that of the alloy. Following prolonged polarization, xps spectra indicated the redeposition of metallic copper from solution on top of the CuCl precipitate.

Surface enhanced Raman scattering (SERS) from benzotriazole adsorbed on brass electrodes

The in situ Raman and SER spectra of 67 33 and 85 15 brass electrodes in 1 N H 2SO 4 solution containing benzotriazole (BTAH) have been investigated using two exciting radiations. The spectra obtained with the 514.5 nm laser line were assigned to a thick polymeric film [Cu(I)BTA] n formed on the brass surface during the dezincification process and were not surface-enhanced. The spectra obtained with the 647.1 nm exciting radiation were attributed to the first layer of the polymeric passive film and were surface-enhanced due to the surface roughness induced by the dezincification process.

The kinetics of spontaneous dissolution of copper-47.3 atom-% brass with hydrogen depolarization: the rate-determining-step

The recent kinetic data of Burzynska and Zembura [1] on the dezincification of brass in deoxygenated sulphuric acid is analyzed mechanistically. It is pointed out that the reported activation energies cannot support the mechanism proposed by them [1] in which crystallization of the copper metallic phase around the copper nuclei (left after preferential dissolution of zinc) is suggested as the rate-determining-step (r.d.s.). It is shown that the data point strongly to the diffusion of Zn atoms in the zinc-rich phases of the brass as the r.d.s.; this proposal would, then, be compatible with the work of Pickering and Wagner [4] and Pickering [5] where solid state diffusion is indicated. It is also remarked that if the dezincification is assumed to be controlled by the cathodic conjugate reaction of hydrogen evolution, with initial discharge as the r.d.s., the expected activation energy would be of similar magnitude as the observed one viz. 19 kcal mol −1; even in this mechanism the crucial importance of the solid state diffusion of zinc is indicated in order to explain the dezincification process.

ChemInform Abstract: Dezincification of Brass and Its Inhibition in Acidic Chloride and Sulphate Solutions.

AbstractThe dezincification process is characterized by the potential‐time relationship, which indicates a selective dissolution of Zn at the initial stage followed by simultaneous dissolution of Cu and Zn and subsequent redeposition of Cu.