Passivation Baths Research Articles

Effective dynamics and fluctuations of a trapped probe moving in a fluid of active hard discs (a)

We study the dynamics of a single trapped probe surrounded by self-propelled active particles in two dimensions. In the limit of large size separation, we perform an adiabatic elimination of the small active particles to obtain an effective Markovian dynamics of the large probe, yielding explicit expressions for the mobility and diffusion coefficient. To calculate these expressions, we perform computer simulations employing active Brownian discs and consider two scenarios: non-interacting bath particles and purely repulsive interactions modeling volume exclusion. We keep the probe-to-bath size ratio fixed and vary the propulsion speed of the bath particles. The positional fluctuations of a trapped probe are accessible in experiments, for which we test the prediction from the adiabatic elimination. We find that for a passive bath the Markovian prediction that the integrated force correlations equal the drag coefficient is not fulfilled in the simulations. However, this discrepancy is small compared to the active contribution and the overall agreement between predicted and measured probe fluctuations is very good at larger speeds.

Regeneration of chromate galvanic solutions in membrane electrochemical devices

The regeneration processes of industry technological passivating baths of electrochemical cadmium lines and electrochemical galvanizing lines as an applied result of two-chamber membrane cation-exchange electrochemical devices researched. Actual industrial passivation baths of cadmium and zinc galvanic coatings applied as anode chambers. The cathode chamber contained sulfuric acid 1 % solution and a titanium cathode (BT-0). A window was cut in one of the walls with a RALEX®CM-PES 11-66 cation exchange membrane placed in it. The lead (С-0) was used as the anode. A comparative analysis of the performance of these technological baths before and after the using cation exchange membrane electrochemical devices was carried out. As a result of long-term experimental studies, the ecological and economic feasibility of their use was proven

Inter-particle ratchet effect determines global current of heterogeneous particles diffusing in confinement

In a model of N volume-excluding spheres in a d-dimensional tube, we consider how differences between the drift velocities, diffusivities, and sizes of particles influence the steady-state distribution and axial particle current. We show that the model is exactly solvable when the geometrical constraints prevent any particle from overtaking all others—a notion we term quasi-one-dimensionality. Then, due to a ratchet effect, the current is biased towards the velocities of the least diffusive particles. We consider special cases of this model in one dimension, and derive the exact joint gap distribution for driven tracers in a passive bath. We describe the relationship between phase-space structure and irreversible drift that makes the quasi-one-dimensional (q1D) supposition key to the model’s solvability.

Dynamics of networks in a viscoelastic and active environment.

We investigate the dynamics of fractals and other networks in a viscoelastic and active environment. The viscoelastic dynamics is modeled based on the generalized Langevin equation, where the activity is introduced to it by means of the exponentially correlated noise. The intramolecular interactions are taken into account by the bead-spring picture. The microscopic connectivity (studied in the form of Vicsek fractals, of dual Sierpiński gaskets, of NTD trees, and of a family of deterministic small-world networks) reveals itself in the multiscale monomeric dynamics, which shows vastly different behaviors in the active and passive baths. In particular, the dynamics under active forces leads to a swelling that is characterized through power laws which are not present in the passive case. In all cases, the dynamics reflects the broad scaling behavior of the density of states and not necessarily the maximal relaxation time of the structures in a passive bath, as it is exemplified on the NTD trees.

Zinc and iron removal from chromium(III) passivation baths by solvent extraction with Cyanex 272

Authors thanked Cytec Ind. for providing a sample of Cyanex 272. Also to the CSIC (Spain) for support.

Protection Mechanism of Al-Rich Epoxy Primer on Aluminum Alloy 2024-T3

The active aluminum-rich primer (AlRP) was invented and developed at NAVAIR to sacrificially protect aluminum alloys and steels from corrosion. The Al pigments (Al-Zn-In) in AlRP were fabricated from a sacrificial anode alloy, which has a lower open-circuit potential than common aluminum alloys. However, initial results indicated that AlRP undergoes severe self-corrosion. Therefore, the Al pigments were pretreated in a trivalent chromium passivation (TCP) bath to reduce the self-corrosion rate. The objectives of this study are to understand the anti-corrosion properties of AlRP on aluminum alloy 2024-T3 substrate and to evaluate the effect of TCP treatment on the Al pigment particles. The polarization curves of AA2024-T3 and active aluminum alloy (Al-Zn-In) show that TCP-treated active aluminum alloy has lower corrosion potential than AA2024-T3 and thus would sacrificially protect it. The AlRPs were exposed in an accelerated exposure test, GMW14872. Exposed samples were then examined using scanning electr...

Improve the performance of Cr-free passivation film through nanoelectrodeposition for replacement of toxic Cr6 + passivation in electrogalvanizing process

To improve the corrosion resistance of Cr-free passivation film on zinc coating for replacing the highly poisonous Cr6+ passivation technology used in electrogalvanizing steels, we synthesized Cr-free passivation film on nanocrystalline zinc coating through a combination of Cr-free passivation and nano-electrodeposition. It was demonstrated that the surface brightness, mechanical strength, scratch resistance and corrosion resistance of zinc coating with Cr-free passivation were significantly enhanced as the coating's grain size was reduced from micro-scale to nano-scale. The nanocrystalline zinc coating after Cr-free passivation treatment exhibits superior properties than the coarse-grained zinc coating experienced conventional Cr6+ passivation treatment. The overall performance of the former is approximately the same as that of nanocrystalline zinc coating with Cr6+ passivation, suggesting that the surface nanocrystallizaiton is more effective than the chemical composition of passivation bath to improve the properties of the passive film. Mechanisms responsible for the improvement in properties of Cr-free passivation film on coarse-grained zinc coating by nano-electrodeposition are analyzed and discussed from the viewpoints of electron localization function and electron work function.

Effect of phase modifiers on boron removal by solvent extraction using 1,3 diolic compounds

AbstractBACKGROUNDAmong the polyols, 1,3 diols are selective and efficient extractants for boron but significant solubility of these into aqueous solutions restricts their application in large scale separation processes. Solvent modifiers can be used to reduce extractant loss to the aqueous phase. Efficiency of the diolic extractants for boron separation have been tested in the presence of different solvent modifiers.RESULTSCompared with other modifiers studied, decanol gives better stability to diolic molecules in the Kerosene phase and exhibits a reduced negative effect on the extraction of boron. Next to decanol, the low viscous 2,6‐dimethyl‐4‐heptanone can be used as solvent modifier.In successive extraction studies, 2‐butyl‐2‐ethyl‐1,3‐propanediol (BEPD) showed better stability among the diols studied in the presence of decanol in the organic phase.CONCLUSIONQuantitative removal of boron was achieved from industrial waste solutions such as a spent phosphate passivation bath and a cutting fluid, using 0.6 mol L−1 BEPD and 0.6 mol L−1 2,2,4‐trimethyl‐1,3‐pentanediol (TMPD) in 25% decanol/Kerosene organic phase. © 2014 Society of Chemical Industry.

Improvement of the electrochemical behaviour of Zn-electroplated steel using regenerated Cr (III) passivation baths

Conversion coatings based on trivalent chromium are more sensitive to the presence of zinc and iron impurities than the chromate formulations. This fact contributes to a decrease in the quality of passivation and to the generation of a significant amount of hazardous liquid waste. Recently, a new eco-innovative process based on Emulsion Pertraction Technology (EPT) is being implemented at industrial scale for selectively removing Zn and Fe from spent passivation baths in order to enhance the lifetime of the Cr (III) baths. In this study, the effect of Zn and Fe removal on the electrochemical behaviour of Zn-electroplated steel samples was evaluated by means of polarisation curves and electrochemical impedance spectroscopy measurements at open circuit potential conditions in 3.5g/L NaCl solutions. The main objective was to assess the benefits brought by EPT using electrochemical methods. Cr (III) passivation baths regenerated using the EPT process have been compared to the bath used in a local industry as well as to fresh and spent baths. According to the results, the samples passivated in the EPT regenerated bath showed a significant improvement in their electrochemical behaviour compared to the samples passivated in the spent baths. This study concluded the suitability of EPT for regenerating Cr (III) passivation baths.

Composition and formation analysis of an ultra-thin antitarnish passive film on electroless Ni-P coating

An ultra-thin passive film on electroless nickel phosphorus coating (ENPC) was obtained by treated in a passivation bath. The antitarnish and corrosion properties of the film were studied by acid exposure and potentiodynamic polarization. XPS was utilized to analyze the chemical composition and formation process of the film. The acid exposure test indicated the antitarnish property of the coating was obviously improved by passivation treatment. The potentiodynamic polarization test showed that the corrosion current for the passivated Ni-P coating was lower than that of untreated coating. By XPS measurement, the thickness of film was evaluated as a few nanometers and the film was made up of Cr, C, O and N. The N and C elements in the film suggested the nitryl aromatic compound should take part in the formation of film. The XPS spectra fitting results indicated that Cr was in the form of Cr2O3 and Cr(OH)3, while O was originated to Cr2O3, Cr(OH)3 and–NO2 in aromatic compound. And the XPS results were used to justify the formation mechanism of the passive film.

Implementation of an eco-innovative separation process for a cleaner chromium passivation in the galvanic industry

Abstract This paper reports the development and implementation of the eco-innovative process Emulsion Pertraction Technology (EPT) for the selective separation of zinc and iron impurities from used trivalent chromium passivation baths. The main goal was to purify the passivating formulations in order to extend their lifetime. Commercial hollow fibre membrane modules were used to provide the non-dispersive contact between the passivation bath and the emulsion extractant phase. Two passivation baths employed at two industrial facilities with initial concentration of metals in the range 3000 0 0 0 2 . The results showed that the effectiveness of EPT was enhanced by the countercurrent operational mode and high flow rates of the emulsion and passivation phases. The performance of the technology for purifying different commercial formulations of chromium (III) baths was proved to be comparable. The best experimental conditions resulted in a decrease of the feed concentration of Zn and Fe of 95% and 98%, respectively, and in a stripping solution enriched in Zn and Fe: 160,000 mg/L of Zn and 49 mg/L of Fe. The process scale-up was evaluated at industrial scale using an EPT unit with a membrane area of 40 m 2 . The mass transfer flux of Zn was 4.5 g/m 2 h, while the flux of Fe was 0.025 g/m 2 h. These values can be used as reference for the scale-up of the process. This work concludes that the implementation at industrial scale indicated the great prospects of EPT on applications in the surface treatment sector. Zinc recovery by electrowinning is recommended.

Environmental Sustainability Assessment of an Innovative Cr (III) Passivation Process

A life cycle assessment was conducted for the Zn-electroplating products passivated by different processes in a small and medium enterprise. The goal was to evaluate and to compare the environmental impact associated to the conventional and alternative passivation process from a “cradle to grave” analysis. The assessment was divided into “cradle to gate”, “gate to gate”, and “gate to grave” steps for natural resources usage and environmental burdens. The innovative process was based on the integration of emulsion pertraction technology to the passivation bath in order to extend its lifetime. Results showed that the transferred hazardous waste from the process to the landfill was the major contributor to the environmental impact of the conventional and innovative passivation. The manufacture of the sodium hydroxide needed in the wastewater treatment process had a main role in the impacts of the “cradle to gate” cycle. This work concluded that the innovative passivation decreased most of the generated waste (92%) during the manufacture cycle of the passivated product as a consequence of the extension of the lifetime of the passivation bath. A reduction of the total environmental burdens to air and to water and the resource usage during the whole manufacture cycle of the product was stated. The environmental burdens to air and to water were mainly connected to the environmental impacts: human health effects and ecotoxicity to aquatic life, respectively.

Integrated use of liquid membranes and membrane contactors: Enhancing the efficiency of L-L reactive separations

Separation processes combining facilitated transport membranes and membrane contactors offer several advantages such as the ability of liquid membranes to promote the uphill transport of target species by the coupling between mass transfer and chemical reaction, together with the benefits of using membrane contactors: large interfacial area, non-dispersive contact and independent flow of the fluid phases that can play an important role in process intensification. In this work, computer simulation techniques using previously validated mathematical models which take into account mass transfer and chemical reaction are employed: (i) to design the integration of liquid contactors in an already existing electroplating process and (ii) to quantify the degree of intensification provided by liquid membrane separation processes through the definition of suitable intensification indexes such as productivity/size ratio and modularity. The methodology has been illustrated through two different real applications in the context of surface treatment industry which were extensively analyzed in previous works: (i) the regeneration of trivalent chromium passivation baths by the on-site continuous removal of zinc and iron trap ions derived from the electroplating process and, (ii) the treatment of spent pickling hydrochloric acid generated in the hot-dip galvanizing process, with the aim of recovering the valuable zinc.

Temperature Enhancement of Zinc and Iron Separation from Chromium(III) Passivation Baths by Emulsion Pertraction Technology

This work reports the influence of the temperature on the selective removal of zinc and iron from a chromium(III) passivation bath by emulsion pertraction technology using Cyanex 272 as extractant and hollow fiber membrane contactors. The results indicate that the kinetics of the separation was largely influenced by the temperature in the range 10–40 °C. The viscosity of the organic liquid phase was measured at different temperatures and extractant concentrations, and the results were fitted to the Riedel and Grunberg and Nissan correlations. The improvement observed from 20 to 40 °C was explained by the increase in the diffusion coefficient of the zinc and iron organometallic complexes through the liquid membrane. However, the remarkably slower zinc and iron separation rates observed at 10 °C in comparison with those at 20–40 °C were attributed to a shift in the driving force due to an endothermic change of the interfacial extraction reaction. The equilibrium parameters at 10 and 20–40 °C were estimated by fitting the experimental kinetic results to the proposed mathematical model. Thus, this work addresses the thermal character of equilibrium and its relevant influence on the separation kinetics of reactive membrane systems.

Zinc recovery and waste sludge minimization from chromium passivation baths

This work reports the feasibility of applying emulsion pertraction technology (EPT) aiming at zinc recovery and waste minimization in the zinc electroplating processes that include Cr (III) passivation. The assessment consists of firstly the lifetime extension of the passivation baths by selective removal of the tramp ions zinc and iron, and secondly, the recovery of zinc for further reuse. Spent passivation baths from a local industry were tested, being the major metallic content: Cr 3+ 9000 mg L −1, Zn 2+ 12,000 mg L −1, Fe 3+ 100 mg L −1. Working in a Liqui-Cel hollow fiber membrane contactor and using the extractant bis(2,4,4-trimethylpentyl) phosphinic acid, reduction of zinc and iron concentrations below 60 mg L −1 and 2 mg L −1, respectively were obtained, while trivalent chromium, the active metal that generates the passivation layer, was retained in the baths. Zinc was selectively transferred to an acidic stripping phase that in the experimental time reached a concentration of 157,000 mg L −1. Zinc recovery by electrowinning from the acidic stripping phase without any pretreatment of the electrolyte solution provided a purity of 98.5%, matching the lower commercial zinc grade. As a result of the extension of the life time of the passivation bath, significant environmental advantages are derived such as minimization of the volume of hazardous wastes and savings in the consumption of raw materials.

Synthesis and evaluation of corrosion resistance of molybdate-based conversion coatings on electroplated zinc

Three molybdate-based conversion coatings on electroplated zinc have been prepared and the composition, morphology, and structure of these coatings are measured by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. It was found that these coatings with ‘meshwork’ surface were complex coatings composed of multiple compounds. Molybdenum species were present in the conversion coating as Mo (VI) and Mo (IV) compounds. The results of neutral salt spray test showed that molybdate-based conversion coatings with the addition of H3PO4, SiO2 and TiOSO4 in the passivation baths possess higher corrosion resistance compared with chromate conversion coatings, which was due to the compactness and anti-corrosion essence of the conversion coating.

The role of liquid membranes in the selective separation and recovery of zinc for the regeneration of Cr(III) passivation baths

® 272 abstract This work aims at the separation of the metallic impurities, namely Zn 2+ and Fe 3+ , from trivalent chromium spent passivation baths used in the galvanic industry by means of selective liquid membranes as an efficient and necessary step in the regeneration of the baths for their useful life extension. A Liqui-Cel hollow fiber membrane contactor separated the spent bath from an emulsion phase constituted of an organic liquid membrane consisting of Cyanex®272, kerosene and 1-decanol and an acidic receiving solution. Real spent passivation baths were used as feed solutions, with complex composition, being the main metallic content: Cr3+ (4500-9350 mg L−1), and Zn2+ (2500-11,780 mg L−1) and Fe3+ (20-93 mg L−1) as tramp ions. The influence of different operational variables on the kinetics of the separation of zinc and chromium as well as on the enrichment of zinc over iron and chromium in the stripping phase was investigated. The variables under study were the pH of the feed mixture, the initial zinc concentration, the carrier concentration in the liquid membrane, and the type and concentration of acid, hydrochloric acid and sulphuric acid used as stripping agent. © 2010 Elsevier B.V. All rights reserved.

Modeling of Iron Removal from Spent Passivation Baths by Ion Exchange in Fixed-Bed Operation

In this work the mathematical model that describes the kinetics of the fixed-bed ion exchange iron separation from chromium(III) passivating baths is presented. Passivation is a common step in the zinc electrodeposition galvanic process. The removal of iron species from the passivation baths allows the extention of their life, thus reducing the amount of waste to be managed and the consumption of raw materials. A commercial chelating resin, Purolite S-957, containing sulfonic and phosphonic acid functional groups was employed. Equilibrium experiments, carried out under isothermal conditions at 20 °C, were correlated to the Freundlich equation, with the following parameters KF ) 25 700((mg (n-1)/n L 1/n )/kgdry_resin) and n ) 2.45. A simple mathematical model assuming a reversible chemical reaction as the rate-controlling step has been developed to describe the fixed-bed iron removal rate in the media solutions under study. The value of the unknown parameter, the rate coefficient for the forward reaction, kd ) 10 660[(mg (n-1)/n L 1/n )/(kgdry_resin h)] was obtained from experimental data of iron uptake employing parameter estimation software. The proposed model offers a satisfactory description of the behavior of the iron loading curves for three different types of real passivation baths under variable feed iron concentration and loading flow rate, using only one estimated parameter.

Selective iron removal from spent passivation baths by ion exchange

AbstractBACKGROUND: Post‐treatment of zinc plated surfaces is required to provide corrosion protection; for this purpose chromium passivation is usually used. In the EU, the older hexavalent chromium passivation baths have been replaced by trivalent chromium conversion coatings. However, the life of Cr(III) passivation baths is reduced due to iron and zinc impurities generated in the process. Thus, the objective of this work was to investigate the regeneration of spent passivation baths from the plating industry by ion exchange using a new chelating resin (Purolite S‐957).RESULTS: Three genuine passivation baths with different iron and zinc concentrations were investigated; the effect of loading flow rate, temperature and resin regeneration conditions on the uptake of iron ions was also studied. The removal performance of iron was increased at higher temperature (55 °C) and lower flow rates. The best regeneration conditions were found to be 6 bed volumes (BV) of 30 wt% HCl.CONCLUSION: This work has shown that iron can be selectively removed from trivalent chromium passivation baths using a new chelating resin (Purolite S‐957) and no addition of chromium (III) is required. Low feed flow rate and high bath temperature (up to 55 °C) are recommended for high iron uptake. Copyright © 2008 Society of Chemical Industry

Exact solution of the Hu-Paz-Zhang master equation

The Hu-Paz-Zhang equation is a master equation for an oscillator coupled to a linear passive bath. It is exact within the assumption that the oscillator and bath are initially uncoupled. Here an exact general solution is obtained in the form of an expression for the Wigner function at time t in terms of the initial Wigner function. The result is applied to the motion of a Gaussian wave packet and to that of a pair of such wave packets. A serious divergence arising from the assumption of an initially uncoupled state is found to be due to the zero-point oscillations of the bath and not removed in a cutoff model. As a consequence, worthwhile results for the equation can only be obtained in the high temperature limit, where zero-point oscillations are neglected. In that limit closed form expressions for wave packet spreading and attenuation of coherence are obtained. These results agree within a numerical factor with those appearing in the literature, which apply for the case of a particle at zero temperature that is suddenly coupled to a bath at high temperature. On the other hand very different results are obtained for the physically consistent case in which the initial particle temperature is arranged to coincide with that of the bath.