Alkaline Degreasing Research Articles

Environmental Effects of Alkaline Degreasing for Automotive, Boat and Machine Industry Purposes

Environmental Effects of Alkaline Degreasing for Automotive, Boat and Machine Industry Purposes

Effect of pretreatment on the interfacial bonding strength between modified polyolefin and aluminum foil treated with trivalent chromium chemical conversion: Experimental, quantum chemical calculations and molecular dynamics simulation

Good adhesive strength and joint durability are necessary for aluminum (Al)/polymer laminated film for lithium-ion battery packages. A pretreatment method involving alkaline degreasing followed by acid pickling was employed to treat the Al foil surface to facilitate the deposition of trivalent chromium [Cr(III)] conversion coating on the surface. The adhesive strength between propylene-based elastomer grafted glycidyl methacrylate (GMA-g-PBE) and Cr(III)-converted Al foil pretreated with 0.5 M HF pickling was 51% higher than Cr(III)-converted Al foil without pretreatment. Moreover, the effect of different pretreatments on the interfacial bond strength of GMA-g-PBE/Cr(III)-converted Al foil was studied from macroscopic to microscopic perspectives. The results indicate that the pretreatment of 0.5 M HF pickling results in complete coverage of the Cr(III) compounds and the formation of a thicker Cr(III) conversion coating on the Al foil compared to other pretreatments. A higher content of Cr(III) compounds results in an increased surface free energy of Cr(III)-converted Al foil, improving the wettability of adhesive melt on the substrate and enhancing the adhesion strength. Moreover, quantum chemical calculations and molecular dynamics simulations were used to investigate the interface bonding mechanism, and the results indicate that GMA in the adhesive exhibits a higher binding energy with Cr(III) oxides and hydroxides compared to Al oxides and hydroxides.

Comparison of Different Surface Pre-Treatment on Mild Steel for Cobalt-Nickel-Iron Electroplating

Electroplating is extensively practiced in the industry to fabricate corrosion-protective coatings for steel in large-scale production. Mild steel easily rusts at ambient temperature thus surface pre-treatment is mandatory to eliminate rust and superficial scale from the steel. Pre-treatment ensures that the steel surface is free from contaminants, which may interfere with the surface quality of the protective coating. This research is done to investigate the effect of different pre-treatment methods on the surface quality of mild steel rings and cobalt-nickel-iron coated mild steel rings. These surfaces were achieved by polishing the ring and subjected to alkaline degreasing, followed by immersion in sulfuric acid or sodium chloride at 10 vol % concentration and different immersion times (50 s, 55 s, and 60 s). Direct electroplating was applied to fabricate the cobalt-nickel-iron coating. The surface morphology of metal substrate and coating after electroplating were tested by scanning electron microscope (SEM), energy dispersive X-Ray (EDS), Vickers hardness, and surface roughness tests. Both types of pre-treatments provided lower surface roughness on the metal substrate and resulted in full coatings without voids formation. The results showed that pre-treatment using sulfuric acid exhibited higher hardness and a smoother coating surface. Agglomerates and cracking were observed on the surface coating treated with sodium chloride.

Microstructural evolution and corrosion behavior of constituent particles of AA2024-T3 Al alloy during zirconium conversion coating

The constituent particles of AA2024-T3 Al alloys were identified and their microstructural change after alkaline degreasing, acidic desmutting, and zirconium (Zr) conversion coating was detailed. The constituent particles of AA2024-T3 included Al-Cu-Fe-Mn, θ-Al2Cu, and S-Al2CuMg, and were several micrometers in size. All these three particles were cathodic to the Al matrix after alkaline degreasing and acidic desmutting pretreatment. The OCP evolution in the Zr conversion bath revealed that the conversion coating reactivity of the as-polished AA2024-T3 was promoted after the pretreatment. The polarization test in 0.1 M Na2SO4 + 0.05 M NaCl solution showed that the cathodic kinetics were enhanced after the pretreatment. Subsequent Zr conversion coating inhibited the anodic kinetics but did not alter the cathodic kinetics in chloride solutions. The defects of ZrO2 coating were responsible for the insignificant change in the cathodic activities.

Fractal Dimension and lacunarity based microscopic image texture characterization of coated and non-coated metallic substrates

ABSTRACT The degree of surface roughness as measured using Fractal Dimension and Lacunarity can serve as quality measures of the coating process. The smoothness of the surface before and after coating is an important characteristic frequently used in surface engineering, to obtain well-polished and smoothened surface finish. We have used Brass plates and coated it with Nickel using electroless and electroplating methods. The images of the coated surfaces were taken using an optical microscope before and after coating. Fractal Dimension (FD) and Lacunarity (λ) of the surface image before and after coating is calculated for comparison using Differential Box-Counting algorithm. Electro-cleaning of the samples in an alkaline degreasing solution is done. Electroplating is carried out in respective electrolytic bath under constant current and temperature conditions. Electroless coating is carried out with a separate Nickel bath at constant temperature of 85° C. The experimental data was validated, which revealed that FD and λ values decreased after coating in all the cases. The lower value of FD and λ after coating suggests more regularity in the surface patterns or smoothness. Hence, we conclude that FD and λ serve as relevant parameters depicting the quality of coating surface at significance level of 0.05.

Surface Modifications Induced by Pretreatments and Effects on The Chemical Structure of TCP Conversion Coating on Al-Cu-Li Alloy (AA2050)

Trivalent Chromium Process (TCP) was developed as a promising conversion process aiming at enhancement of corrosion properties and adhesion of aluminium alloys. The alkaline etching and acid pickling are usually applied as surface pretreatments on aluminium alloys before TCP deposition in order to optimize their properties. In this work, the surface modifications of an Al-Cu-Li alloy (AA2050-T8) at different stages of pretreatment (alkaline degreasing and acid pickling) and subsequent TCP are investigated by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy. The pretreatments leading to significant enrichments in Cu and less marked in Ag, show also a strong influence on the subsequent formation of TCP in comparison to the non-pretreated, polished AA2050-T8 alloy. A slight decrease in Li content is observed in the oxide layer after pretreatment and no Li is present in the outer TCP layer. A thicker TCP conversion coating (outer oxide) with less cracks is formed on the pretreated alloy surface than on the polished one. Moreover, a Cu enrichment is evidenced in the TCP layer of the pretreated sample, which results in enhanced cathodic activity of pretreated sample with reference to polished sample as demonstrated by linear sweep voltammetry.

Sustainable Sandwich Panels Made of Aluminium Skins and Bamboo Rings

This work investigates the mechanical behaviour of a sustainable sandwich panel, consisting of bamboo rings core, treated aluminium skins and epoxy adhesive. A Design of Experiment (DoE) is used to identify the effects of bamboo diameters (30 and 45 mm) and aluminium skin treatments (alkaline degreasing and application of primer) on the mechanical and physical properties of sandwich panels. The aluminium skins treated with the wash primer significantly increase adhesion to the polymer, resulting in greater maximum load, flexural strength, maximum skin stress and maximum core shear stress; while the skins treated with NaOH resulted in a greater flexural and core shear modulus. Relatively more rigid and resistant structures are obtained with Ø30 mm rings, due to the increased surface contact area and the number of constraints on the core. The samples fail due to the skin fracture, implying an efficient face-core bond that is attributed to the proper absorption of the polymer by bamboo and the treatment of the aluminium surface. The proposed panels present good mechanical performance, proving to be a feasible and promising alternative for secondary structural applications.

Investigation of Electroless Plated Magnetic Thin Film for Application to Medical Magnetic Devices

Recently, pandemics due to new viruses and pathogens have occurred worldwide. New species of viruses and pathogens are less effective than conventional drugs, so more effective treatments are needed. A tailor-made drug discovery research has been actively investigated. Human immune cells have cells called B lymphocytes. If we can analyze the immune mechanism by stimulating B-lymphocytes with antigens, identifying and capturing cells that respond to B-lymphocytes, we can develop highly efficient and low side effect drugs that are effective only against the causative pathogens. Therefore, a method to capture B lymphocytes modified with magnetic beads on magnetic micro-spot arrays by magnetic force is proposed. This method has been shown to be one of the most promising candidates for obtaining accurate genomic data because it can capture cells more rapidly than conventional capture methods. However, this method requires a perpendicular residual magnetic flux density (Mr⊥) in the perpendicular magnetic field that does not allow the B lymphocytes to flow out, because, although it is possible to capture B lymphocytes when a magnet is installed, there is a problem that the B lymphocytes flow out during the subsequent rinsing process. In this study, the plating conditions were investigated to improve the perpendicular magnetic anisotropy of cobalt (Co) based magnetic thin films. Alkaline degreasing and acid-activated copper (Cu) plates were used as substrates for the experiments. CoNiP, CoNiMnP and CoNiMnReP thin films were prepared by electroless plating under the plating bath composition and plating conditions as shown in Table 1. Vibrating sample magnetometer (VSM), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDS) were used for the evaluation. Fig. 1 shows the hysteresis curves of thin films plated with different bath compositions. Perpendicular residual magnetic flux density (Mr⊥) was 25 emu/cc for the CoNiP thin film and 219 emu/cc for the CoNiMnP thin film.The CoNiMnP thin film was found to improve Mr⊥ more than 8 times compared to the CoNiP thin film.It was found that the addition of MnSO4 5H2O improved the Mr⊥.The addition of MnSO4 5H2O may have enhanced Mr⊥ due to the effect of crystal magnetic anisotropy due to the vertical orientation of the c-axis of hcp Co.The perpendicular saturation magnetic flux density (Ms⊥) values were 818 emu/cc and 612 emu/cc for the CoNiMnP and CoNiMnReP thin films respectively.The results showed that the addition of NH4ReO4 reduced the Ms value with maintaining a high Mr⊥ values. Figure 1

Effect of the Application of Different Surface Treatment Methods on the Strength of Titanium Alloy Sheet Adhesive Lap Joints.

This study investigated the effect of the different surface treatment methods on the strength of Ti6Al4V titanium alloy sheet adhesive joints. The following surface treatment methods were used: alkaline degreasing, anodizing, vibratory shot peening, and anodizing with vibrational shot peening. The following tests/measurements were carried out during the experiment: surface roughness measurements; microhardness measurements (conducted by the Vickers hardness test method); and strength tests of single-lap adhesive joints fabricated with the use of two epoxy adhesives, rigid and flexible, both based on epoxy resin Epidian 5. It has been found that the application of anodizing followed by vibratory shot peening leads to increased strength of adhesive joints, irrespective of the type of applied epoxy adhesive.

Physical Properties of Deposits and Three-Dimensional Structures Prepared By High-Speed Electrolytic Copper Plating Using a Jet Flow Device

Since copper has excellent properties such as malleability and conductivity, it is widely used in the electronics field. Copper sulfate plating is expanding further in fields requiring thick deposits such as for heat dissipation boards and bumps for stress relaxation during semiconductor mounting. In order to improve productivity and reduce cost, high speed electroplating using high current density is desired. However, in electroplating under high current density, abnormal deposition such as burnt deposits and dendrites due to insufficient supply of the metal ion. In order to facilitate the supply of the metal ion, our group focused on mechanical agitation type jet devices rather than conventional air or paddle agitation. In this study, the physical properties of deposits prepared by conventional copper sulfate plating at 5 A/dm2 and the high speed copper plating at 30 or 50 A/dm2 were compared. Furthermore, the high-speed copper sulfate plating method was applied to wiring and bump resist patterns where production of three-dimensional structures was demonstrated. 20×30 mm cut copper plates were used as the test substrate, which were treated with the alkaline degreasing and the acid activation prior to plating. Three kinds of additives Bis-(3-sulfopropyl) disulfide (SPS), Janus Green B (JGB) and Polyethelene glycol-20000 (PEG-20000) were used in the copper sulfate plating solution. Samples were annealed at 120°C for 60 min after plating. Investigation of physical properties was conducted by comparison of crystal orientation measured by X-ray diffraction (XRD) and electrical conductivity measured by sheet resistance. Furthermore, the etching rate of each film was calculated from the mass loss per unit etching time. The additives were optimized for preparation of the three-dimensional structures. The current density was swept at an arbitrary speed from 0 A/dm2 to a target current density, and once reached, the current density was maintained until the target film thickness was obtained. The test substrate after plating was subjected to resist observation and then to observation using a scanning electron microscope (SEM). Fig. 1 shows the crystal orientation attained at each current density. It was confirmed that both films produced at the current densities of 30 and 50 A/dm2 by high speed copper plating and the film produced at 5 A/dm2 using the conventional method were oriented with 60% of the 111 crystal phase. The sheet resistance values of all three films exhibited approximately the same value of 0.93 to 0.95 Ω/sq. . On the other hand, the etching rate of the films produced by high-speed copper plating were 2.5 µm/min, whereas that of the film produced by the conventional method was 1.7µm/min. Fig. 2 shows the wiring pattern filled with 30 A/dm2. It was confirmed that pattern filling by high speed plating can be accomplished 10 times faster than with the conventional method. Resist pattern filling by plating at higher current density will be discussed in detail. The high-speed copper plating film using a jet flow device has the near physical properties as the conventional method. Furthermore, since filling of the pattern substrate can be performed in a short time, it is considered that it can contribute to improvement of productivity in the electronic field. Figure 1

Study on the Viability of the Recycling by Electric Arc Melting of Zirconium Alloys Scraps Aiming the Scalability of the Process

Turning chips of zirconium alloys are produced in large quantities during the machining of alloy rods for the fabrication of the end plugs for the Pressurized Water Reactor (PWR) fuel elements parts of Angra II nuclear reactor (Brazil – Rio de Janeiro). This paper presents a study on the search for an efficient way for the cleaning, quality control and Vacuum Arc Remelting (VAR) of pressed zirconium alloys chips to produce a material viable to be used in the production of the fuel rod end plugs. The process starts with cutting oil clean out. The first step in this process consists in soaking a bunch of chips in clean water, to remove soluble cutting oils, followed by an alkaline degreasing bath and a wash with a high-pressure flow of water. Drying is performed by a flux of warm air. The oil free chips are then subjected to a magnet in order to detect and collect any magnetic material, essentially ferrous, that may be present in the original chips. Samples of the material are collected and then melted in a small non consumable electrode vacuum arc furnace for evaluation by Energy Dispersive X-ray Fluorescence Spectrometry (EDXRFS) in order to define the quality of the chips. The next step consists in the 15 ton hydraulic pressing the chips in a die with 40 mm square section and 500 mm long, producing an electrode with 20% of the Zircaloy bulk density. The electrode was finally melted in a laboratory scale modified VAR furnace located at the CCTM–IPEN, producing 0.8 kg ingots. The authors conclude that the samples obtained from the fuel element industry can be melting in a VAR furnace, modified to accommodate low density electrodes, allowing a reduction up to 40 times the original storage volume, however, it is necessary to remelt the ingots to correct their composition in order to recycle the original zirconium alloys chips. in a process to reduce volume and allow the reutilization of valuable Zircaloy scraps.

Selective deposition on electrodes of chip component by electroless plating method

The selective electroless deposition on metallic electrodes of a micro-passive-chip component was investigated. We performed three pretreatments: (a) alkaline degreasing, (b) acid activation, and (c) catalytic activation by the double alternate-dipping method consisting of two steps, i.e., sensitization (SnCl2) and activation (PdCl2). Catalytic conditions such as the concentration of PdCl2, activation time, and number of activation times were optimized to achieve the selectivity of electroless deposition. The mechanism of the selectivity of electroless deposition was investigated by X-ray photoelectron spectroscopy measurements. Tetravalent Sn and metallic Pd are observed on the inner electrode of the sample. On the other hand, metallic Sn and tetravalent Pd are mainly observed in certain areas except the inner electrode areas. These results indicate that the sensitization is performed well in the inner electrode region because Pd must be in a metallic state to validate its catalytic activity.

Al-Zn Alloy Formation from Non-Aqueous Solution By Electrochemical Technique

Introduction At present, the hot dipping of Zn-Al, uses to suppress the corrosion of the steel. In addition, Al-Zn alloy become a high strength material such as duralumin by making the alloying with Mg and Cu. An aluminum, that is less noble than hydrogen is, not able to be electrodeposited from aqueous solution.1)Therefore, the electrodepositions using ionic liquids or non-aqueous have been studied. However solution such as toluene, which has a risk of causing a spontaneous combustion because of it’s high flammable. An ionic liquids are salts whose melting point less than 100 ℃. Since the solution has very high electrical conductivity, high stability and, low volatility, it is suitable for plating solvent. In this study, we report on the results of the plating of the Al-Zn alloy films from the plating bath with AlCl3, ZnCl2 and dimethyl sulfone (DMSO2). Experiment The plating solution was composed of AlCl3, ZnCl2 and DMSO2. The total metal chloride ratio, (AlCl3 + ZnCl2) / (DMSO2 + AlCl3 + ZnCl2), is constant at 33.3 mol%. The ratio of ZnCl2 to AlCl3 is controlled from 0.005 to 1.0 mol%. A current density is 600A/m2. The acid activating (RT, 1min) after alkaline degreasing (60 ℃, 5min) is performed as pretreatment process. The plating was performed at 150 ℃ for 30 minutes. As analysis method of sample, we used X-ray diffraction (XRD), energy dispersive x-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS). Results and Discussion Effect of bath composition As a result of changing the bath composition, metallic gloss plating film was deposited up to 0.05 molar percent metal salt concentration of Zn. The gray film was obtained in 1.0 molar percent.Results of by EDS The composition of the deposited Al-Zn alloy plating films was estimated by using EDS. The content of Zn is increased with increasing the concentration of the metal salt Zn. Result by X-ray diffraction (XRD) Figure 1 shows an XRD pattern of the sample. The peak of the Al can observed without the sample of 0.1 molar percent of Zn salt. Figure 2 shows an enlarged view of Al (200) peak area. With increasing of the Zn metal salt concentration, the diffraction peak is shifted to a lower angle side, and the half width is increased. An atomic radius of Zn and Al are 125 and 135 pm, respectively. The diffraction peak will be shifted to high angle in accordance with Vegard’s low, when Zn is replaced by Al site. The increase of half width shows deterioration of crystallinity. Acknowledgements This work was partially aided by MEXT-supported Program for the Strategic Research Foundation at Private Universities. References T. Hirato, J. Fransaer, and J. P. Celis, J. Electrochem.Soc., 148, C280 (2001).

Metal-ceramic bond mechanism of the Co-Cr alloy denture with original rough surface produced by selective laser melting

The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal(PFM) restorations. Surface roughening methods, such as sand blasting, acid etching and alkaline degreasing for the metal matrix are used to increase bond strength. However, the metal matrix of PFM processed by selective laser melting(SLM) has natural rough surface. To explore the effect of the original roughness on metal-ceramic bond strength, two groups of specimen are fabricated by SLM. One group of specimen surface is polished smooth while another group remains the original rough surface. The dental porcelain is fused to the specimens’ surfaces according to the ISO 9693:1999 standard. To gain the bond strength, a three-point bending test is carried out and X ray energy spectrum analysis(EDS), scanning electron microscope(SEM) are used to show fracture mode. The results show that the mean bond strength is 116.5 ± 16 MPa of the group with rough surface(R a=17.2), and the fracture mode is cohesive. However, when the surface is smooth (R a=3.8), the mean bond strength is 74.5 MPa ± 5 MPa and the fracture mode is mixed. The original surface with prominent structures formed by the partly melted powder particles, not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect. Statistical analysis (Student’s t-test) demonstrates a significant difference (p<0.05) of the mean value of bond strength between the two groups. The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value (25 MPa) of the ISO 9693:1999 standard. It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.

Evaluation of a sulfursilane anticorrosive pretreatment on galvannealed steel compared to phosphate under a waterborne epoxy coating

Galvannealed coatings are produced by annealing zinc hot dip coated steel where iron and zinc undergo interdiffusion to form iron–zinc alloys. They offer some attractive features like better weldability, paintability, corrosion resistance, ductibility and formability, depending on the morphology, composition and structure of the coating phases. Silane films are a good choice to replace phosphate pretreatment, and in the case of bis-sulfursilane films, the sulfur chains also help to increase the hydrophobicity of the film and its protection against corrosion. Epoxy coatings are reasonably corrosion resistant and generally applied as primers or direct-to-metal (DTM) coatings in coating systems for different metallic substrates.Using the optimum conditions previously determined for obtaining a 3% bis-1,2-[triethoxysilylpropyl] tetrasulfide (BTESPT) solution in a water/ethanol solvent at pH 4 hydrolyzed in the presence of 50ppm Ce(IV) ions, the silane solution was applied on galvannealed steel samples by dip coating process with samples remaining immersed for 15min before being withdrawn and cured for 40min at 150̊C. The bare galvannealed samples were previously treated, first by sonication in acetone and then by a commercial alkaline degreasing solution. The phosphate samples were prepared in an industrial set using the tricationic bath containing Mn, Zn and Fe phosphates.The waterborne epoxy coating was applied with a brush to reach a 60±6μm dry film thickness layer. The evaluation was performed by electrochemical technique: EIS, electrochemical impedance spectroscopy, and also by accelerated tests in a salt spray cabinet (SSC). The silane, phosphate and non-treated samples were tested in 3.5wt% NaCl solution in a cell of 20cm2 after 3h, 24h, 96h, 264h, 360h, 528h and 720h of immersion in the electrolyte solution. The results indicated that the silane pre-treated samples have shown the highest impedance modulus value even after 530h of immersion.Adherence and flexibility were also evaluated by tape test–X method–and conic mandrel test. The results have evidenced the superior adherence of the coating for the silane pre-treated samples. The SSC test revealed that the silane pretreated samples showed less blistered area around the scratch.In summary, the sulfursilane pretreated samples presented an overall better performance concerned to the corrosion resistance compared to phosphate and waterborne epoxy coated galvannealed steel samples.

Mild steel corrosion in chloride environment: effect of surface preparation and influence of inorganic inhibitors

The aim of the present work is to study the effect of surface mild steel preparation on its electrochemical behaviour in neutral chloride solution without and with an inorganic inhibitor. Various surface preparations are examined: alkaline degreasing, acid pickling and polishing. Open circuit potential measurements and potentiodynamic polarisations are used as corrosion monitoring techniques. The effect of chloride concentration is evaluated. The ability of inorganic inhibitors (Na2MoO4, NaNO2, Na2WO4 and Na2VO3) to stabilise the passive state of steel in chloride containing solutions is assessed by electrochemical and surface analysis techniques. The results reveal that, among the four inhibitors studied, the sodium molybdate is the best environmentally friendly corrosion inorganic inhibitor for steel.

Aplicação de SAM em liga de alumínio AA 2024-T3 com desengraxe alcalino

As moléculas auto-organizáveis (SAM - Self Assembly Monolayer) são inibidoras de corrosão, devido à capacidade de se organizarem sobre superfícies formando filmes finos. A SAM apresenta elevada afinidade pelo óxido formado sobre o alumínio, porém as interações entre a camada de óxido e as SAM nem sempre são satisfatórias, pois o óxido formado na superfície apresenta heterogeneidades, que interferem na formação do filme de SAM. O objetivo desse trabalho foi estudar a proteção à corrosão do alumínio AA 2024-T3 associada ao SAM, após tratamento com desengraxante alcalino. A caracterização eletroquímica foi realizada por espectroscopia de impedância eletroquímica e polarização potenciodinâmica anódica em meio de Na2SO4 0,5 mol. L-1 em pH 4,0. A morfologia superficial foi investigada por microscopia óptica. Os resultados mostraram que as SAM promoveram maior proteção do alumínio, quando este foi pré-tratado com o desengraxante.

The influence of alkali‐degreasing on the chemical composition of hot‐dip galvanized steel surfaces

AbstractThe influence of dipping temperature and time on the surface chemistry of hot‐dipped galvanized steel sheets during the alkaline degreasing process is investigated. The surface chemistry was monitored with scanning Auger electron spectroscopy (AES), X‐ray photoelectron spectroscopy (XPS), and time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS). The results show high Al concentrations on the untreated surfaces, which are significantly reduced during alkaline degreasing. The same conclusions could be drawn for the carbon compounds that accumulate on the surface during storage. The measurements reveal a gradual reduction in surface Al as the alkali solution temperature and/or degreasing time are increased. When degreasing was conducted at 70 °C for 30 s the surface was practically free from Al, which was present only in small islands. Furthermore, the experiments showed that the thickness of the oxide film covering the surfaces before and after alkaline degreasing is approximately 20 Å. The main constituents of the film varied from ZnAl hydroxide/oxide to Zn hydroxide/oxide, before and after degreasing, respectively. Copyright © 2006 John Wiley &amp; Sons, Ltd.

An electrochemical study of the delamination of polymer coatings on galvanized steel

The relationship between the rate of polymer delamination and the intensity of either anodic or cathodic current under the paint has been investigated for the zinc/surface treatment/polymer system by using a special electrochemical cell. Three types of surface treatment were investigated: simple alkaline degreasing, trication phosphating, and a chromate free conversion coating. Significant differences were observed for the three substrates. The alkaline resistance of the conversion coatings was determined using an ICP atomic emission spectroelectrochemical method. The results are interpreted in terms of the differing chemical stability of the conversion layers towards hydroxide generated by oxygen reduction.

Continuous regeneration of degreasing solutions from electroplating operations using a membrane bioreactor

To extend the service life and to improve the quality of degreasing solutions from surface refining processes in the metal working industry a process based on a membrane bioreactor (MBR) with submerged multi-channel flat sheet ceramic membranes was developed. This MBR-based regeneration process combines the retention by membranes and the biodegradation of oils/grease. The objective is to retain the biomass as well as the hydrocarbons in the bioreactor by the microfiltration membranes to enhance biodegradation. Simultaneously, low retention is aimed at for the surfactants since these substances have to be returned to the degreasing bath. The process was tested with a mobile pilot plant over a three-month period on site in an enterprise which carries out electroplating on commission. The multi-channel flat sheet ceramic membranes, which had an average pore diameter of 0.3 μm, fulfilled the objective of retaining the hydrocarbons to a high extent while allowing relatively high permeation of the surfactants (in order to minimise additional dosing). Permeate was free of solid matter and hydrocarbon concentration was reduced by 85–90% (compared to the feed). The reduction in non-ionic surfactants was only 25–40%. Compared to conventional (“open”) biological regeneration, a five fold increase in volumetric biodégradation rate was achieved due to the higher biomass concentration. A preliminary economic analysis for this case study showed, that there was a reduction in costs of roughly one third for the process under study in contrast to conventional hot alkaline degreasing. The main reason for this saving is the lower cost of wastewater treatment.