Role of Thiamine Hydrochloride and Gelatin on the Electrodeposition of Zinc

A search for a non-cyanide zinc plating bath resulted on the development of a zinc acetate bath. To obtain bright zinc deposits, thiamine hydrochloride and gelatin were added. Hull cell studies revealed that in presence of 3 g dm^?3 thiamine hydrochloride a bright deposit was obtained at a current density above 2.5 A dm^?2. Addition of 3 g dm^?3 gelatin produced a bright yellow tinge deposit above 2.5 A dm^?2. Voltammetric studies carried out at a glassy carbon electrode in the plating solution revealed that in the pH range of 4.5-5.5, zinc acetate complexes underwent successive reduction to zinc. Acetate ions and pH affected both the dissolution and deposition of zinc. The dissolution of zinc took place with the participation of OH^? ions. Gelatin molecules adsorbed on the electrode surface. They favoured both zinc dissolution and deposition and prevented hydrogen evolution in the potential range of interest. Thiamine hydrochloride caused a reduction in zinc dissolution and deposition rates but favoured hydrogen evolution.     

Arc weldability of zinc coated steel sheets

Summary

CO₂ arc fillet welding of lap joints in zinc coated steel sheets and Zn-Fe coated steel sheets produced from base metals with a different surface roughness is performed to clarify the relationship between the properties of zinc coating layers and the factors affecting the generation of pits and blowholes during arc fillet welding of lap joints in zinc coated steel sheets. The results show that the generation of pits and blowholes is sharply reduced with a decreasing Fe content in the zinc coating layer and the decreasing surface roughness of the base metal. A reduction in the Fe content of the zinc coating layer decreases the melting point of the zinc coating layer, causing the zinc coating layer to melt faster and enabling the molten zinc to escape faster from the molten pool. A reduction in the surface roughness of the base metal increases the mobility of the molten zinc on its surface near the molten pool. When zinc coated steel sheets with a zinc coating weight of 40 g/m² produced from smooth surface base metal (Ra = 0.1 μm) were welded at a welding speed of 1.0 m/min, the generation of pits and blowholes was strongly suppressed to the same level as found during corresponding welding of cold-rolled steel sheets.     

Development of High Speed Lead Plating and its Applications

A high speed lead plating process has been developed. The bath contains, per gal US, Pb(BF₄)₂ 62·5 oz, HBF₄ and H₂BO₂ ach 6 oz and hydroquinone 1·3 oz. The optimum temperature is 160°F and cathode surface velocities of 0–150 ft/min have been evaluated. Limiting current densities up to 3100 A/ft² and average operating current densities up to 1000 A/ft² are possible. Deposits are fine grained and cover basis metal defects even with coatings 0·1 mil or less. Brushing the basis metal and especially interrupting the lead deposition to brush the deposit reduces porosity. Coatings 0·05 to 0·1 mil thick so produced on steel when tested resisted corrosion by shellac better than terne and tinplate and were satisfactory in water-base paints. However, lead coatings on steel have poor solderability. Salt spray tests confirm the superiority of the deposits produced from the hydroquinone bath with or without brushing treatments. Copper and tin strikes were of no value in corrosion or solderability tests. Power and metal cost is lower for the lead coatings than for zinc coatings of equal thickness. Production facilities for lead-plating steel strip of various gauges are discussed.     

Electrochemical codeposition of PMMA particles with zinc

Zinc matrix composite coatings containing polymethyl methacrylate (PMMA) particles were electrodeposited from an aqueous acidic (pH 2.0 and 4.0), lignosulfonate solution of zinc sulfate on low-carbon steel substrates, under galvanostatic, either constant or pulse current, plating conditions at current densities of 2 and 20 A dm⁻². The effect of particle inclusion on the deposit electrocrystallization was investigated by X-ray diffraction and scanning electron microscopy. The observed dependence of the PMMA content of the deposits on bath pH and applied current density was illustrated in terms of the particle surface charge variation and their interaction with the growing metal phase. The corrosion resistance of the composite coatings was evaluated by Tafel analysis.     

Corrosion inhibition of mild steel in sodium chloride solution by some zinc complexes

The corrosion inhibitive effect of zinc acetate, zinc acetylacetonate and zinc gluconate on the mild steel immersed in 3.5% NaCl solution was evaluated by electrochemical impedance spectroscopy (EIS). The results revealed superiority of zinc gluconate whilst zinc acetate showed inferior corrosion inhibition. The surface of the samples exposed to the inhibited solutions was analyzed using XRD and SEM techniques. The pH measurement of the test solutions before and after corrosion, also before and after addition of Fe⁺² and Fe⁺³ revealed that the superior inhibition of zinc gluconate is related to formation of insoluble corrosion products on the mild steel surface.     

Effect of zinc plating of low carbon steel on corrosion resistance in cassava fluid environment

Abstract

This research work investigated the corrosion resistance of zinc plated low carbon steel in cassava fluid (i.e. containing hydrogen cyanide). It simulated the effect of continuous use of the material in a cyanide environment where corrosion products are left in place. Low carbon steel samples were zinc electroplated at voltages between 0˙5 and 0˙9 V for 5 to 20 min. The plated samples were then subjected to a cassava fluid environment for 30 days. The electrode potentials, in mV (SCE), were measured every day. Weight loss was determined at intervals of 5 days for duration of the exposure period. The result showed corrosion attack on the zinc plated steel, the severity increasing with increasing weight of zinc coating on substrate. The result showed that thinly plated low carbon steel did not have any advantage over unplated steel and were quickly stripped of their zinc plating with resultant corrosion of the underlying steel substrate. Heavily zinc plating steel was observed to offer some protection for the steel but not for a long time. The pH of the cassava solution which initially was acidic because of the cyanide content in the cassava was observed to progress to neutrality after 5 days and then became slightly alkaline at the end of the 30 days test (because of corrosion product contamination of the cyanide), contributing to the reduced corrosion rate. Unplated steel was found to be unsuitable for the fabrication of cassava processing machinery without some form of surface treatment, but unfortunately, zinc is not suitable as a protective coating in this environment.     

Untersuchungen über Korrosionsvorgänge an Stahl nach einmaliger Chlorid-Kontamination

Investigations into the corrosion processes on steel after one-time's chloride contamination Investigation of chloride adsorption and desorption on mild steel St 37 (1.0120) and austenitic stainless steel X 5 CrNi 189 (1.4301) showed chloride adsorption layer, determined radiochemically, depends upon the material, the state of metal surface layer, and its pretreatment. Ground surface of St 37 retains comparatively less chloride ions on washing than an unpretreated specimen. On the other hand the chloride could be removed from the austenitic steel by rinsing twice in unagitated washing medium which lowered the chloride content to below the detection level of 0,02 m?g Cl^?/cm². Corrosion behaviour of specimens of 1.4301 in autoclave showed no difference with regards to corrosion in the test cycles of 300 and 400 h at 150 and 200° C whether or not the specimens were contaminated by chloride. Mild steels whose state of surface is similar to St 37 should be guarded against chloride contamination to prevent delayed damage. In case of steel similar to 1.4301 with regards to their surface characteristics cleaning the surface is relatively easy. Long time tests to assess risks of delayed damage are in progress and will be communicated later.     

Atmospheric corrosion of zinc induced by runoff

Atmospheric corrosion and runoff of zinc were investigated during two years in humid tropical climate on hot dip galvanized steel and zinc samples. The high zinc mass loss (14.70 g m⁻²) is induced by the intensive zinc release (12.40 g m⁻²). No corrosion phase containing chloride was detected on the zinc surface, while a variety of sulfates not dissolved by rains reveals the sensitivity of zinc to SO₂ pollutant. However, two chloride-containing corrosion products were detected on the galvanized steel. Exponential equation is proposed that fits well the experimental data for zinc mass loss induced by runoff process as a function of the time of wetness. The formula gives possibility to predict the mass loss even before a steady state in the corrosion process has been reached. This equation can converge to a Benarie lineal function (C = At_w), when the coefficient b = 1 for the corrosion which is accelerated with the partial removal of the corrosion layer during the runoff phenomena.     

Zinc runoff from galvanised steel materials exposed in industrial/marine environment

Abstract

An investigation has been carried out to assess the zinc runoff from a variety of galvanised materials over 16 months at the industrial/marine Port Talbot weathering site. Over 16 months of exposure, bare zinc, and Electrozinc have the highest levels of zinc runoff (4·38 and 4·20 g m^-2) followed by general galvanised steel substrates, i.e. hot dip galvanised (HDG) steel (0·15 wt-%Al) (2·87 g m^-2) and iron zinc intermetallic galvanised steel (galvanneal, 2·36 g m^-2). Galvanneal (IZ) has a higher initial runoff rate than HDG due to the presence of iron/zinc intermetallic in the coating that promotes anodic zinc dissolution. The HDG has a more constant runoff rate that exceeds IZ after 7-8 months due to build up of corrosion products on the IZ surface. Aluminium/zinc alloy coated steels have a much lower runoff rate than general galvanised materials as the aluminium present in the structure provides a strongly protective oxide barrier coating improving corrosion resistance (Galfan 5 wt-%Al, 2·04 g m^-2, and Z alutite 55 wt-%Al, 0·67 g m^-2). Organically coated steels show relatively little zinc runoff (< 0·25 g m^-2) indicating their effectiveness in preventing surface corrosion. Runoff levels measured do not exceed permissible levels of zinc for drinking water and the measured zinc runoff levels pose little threat to organisms if leached into soil. Using an accelerated laboratory test in which distilled water is sprayed onto specimen panels in a recirculatory system for 100 h a good correlation can be obtained with external exposure for up to 6 months exposure. For 12 months exposure iron zinc intermetallic galvanising (galvanneal) begins to become covered in a protective oxide layer, which cannot form under the conditions of the accelerated test. Despite this, the fit for most specimen types is excellent. Where the predictive test fails is when the galvanising layer is breached revealing an efficient iron cathode site. This occurs first for electrocoated zinc after 16 months exposure. Similar predictive results can be obtained using a scanning vibrating electrode technique (SVET) in a semiquantitative manner and an immersion electrolyte of 0·1 wt-%NaCl. Again the predictions are initially very accurate but following 12 months exposure the fit for specimens of electrozinc is poor due to the breaching of the galvanising layer.     

电镀锌钢板的黑变机理

在发现铅是导致电镀锌钢板黑变发生的关键因素的基础上 ,对电镀锌钢板的黑变机理提出了锌铅共沉积假说和硫酸铅胶体膜假说 ;并对不同工艺中获得的电镀锌钢板进行了黑变培养 ,通过丁达尔和界面电泳实验研究了铅在硫酸锌溶液中的存在形式 ,通过钝化及破胶实验研究了钝化工艺和镀后清洗对黑变的影响 ,验证了黑变是由于硫酸铅胶体膜在镀锌层外表面被吸附而造成的。     

Zinc corrosion runoff process induced by humid tropical climate

Zinc and hot dip galvanized steel are frecuently used metals in building application. They have relatively good atmospheric resistance to corrosion, due to its oxidation in air and formation of protective rust on its surface, which acts as barrier between the metal and environment. However, some part of the rust can be dissolved by pluvial precipitations and water condensed on the metal surface. This process, called metal runoff, contributes for zinc dispersion in soils and waters. In order to make accurate estimation of zinc runoff induced by atmosphere in humid tropical climate, samples of pure Zn and hot dip galvanized steel have been exposed in the Gulf of Mexico. The data reveal that this process is strongly influenced by factors which determine the aggressivity of the environment (pluvial precipitations, cycles of dry and rainy periods, atmospheric pollutants, air humidity). High annual rates of zinc runoff (6.5 – 8.5 ± 0.30 g Zn m^?2yr^?1) were released, being the runoff 63 – 87% of the zinc corrosion rust. The zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO₂ as the major factor controlling the runoff of zinc. The reported results show higher runoff of zinc samples, compared to that of hot dip galvanized steel     

Optical visualization of concentration field of Zn during galvanic corrosion of a Zn/steel couple

We applied shadowgraphy and Mach-Zehnder interferometry to investigate concentration field of Zn²⁺ above a Zn/steel couple in 0.01 M NaCl. During galvanic corrosion, the marked changes in the concentration of Zn²⁺ were visualized in a thin solution layer less than 0.5 mm thick above zinc. The concentration profile of Zn²⁺ was also obtained by analyzing the deflection of interference fringes. The obtained concentration profile was in good agreement with that obtained by our group with a scanning probe technique. The formation of zinc corrosion products was also visualized, which occurring on the steel surface a certain distance away from zinc.     

Die Korrosionseigenschaften von feuerverzinktem Stahlblech in warmen weichen Wässern mit CO2- und/oder O2-Spülung

Corrosion properties of hot dipped galvanized steel plating in soft warm water with CO₂ and/or O₂ flows Research has been carried out on hot dipped galvanized plates in warm (70° C) diluted NaCl and Na₂SO₄ solutions with a conductivity of 300 μ S/cm at room temperature as a function of the composition of the flowing gas. When exposed to oxygen, the specimen plates show marked pit corrosion already after a few days. An attack on the zinc layer is followed by a local attack on the bared surface of the steel. Cathodic protection by sacrificial magnesium anodes, whilst reducing the corrosion rate, gives rise to needle-prick pitting corrosion on the zinc layer. The only means of stopping corrosion completely is the application of external current protection with several amps pr. sq. metre. With carbonic acid flow, the zinc layer is removed homogeneously, the corrosion rate being of the order of 0.07 μ/h. In the case of gassing with a 1 : 1 mixture of carbonic acid and oxygen, a corrosion-inhibiting covering layer of hydrozincite is formed. Hot dipped galvanized specimens with a zinc cover of approx. 47 μ showed no signs of corrosion after 4350 hours. In no case was it possible to observe a reversal of the potential of the iron-zinc element. The pitting corrosion encountered with oxygen flow must be ascribed to the effect of Evans' elements.     

The Electrodeposition of Iron-Zinc Alloys

Methods are given for depositing iron-zinc alloys of 3 to 90% zinc content from sulphate baths and attention is drawn to the useful properties of these deposits. Under a given set of plating conditions the iron-zinc ratio in the deposit is directly proportional to that in the bath. Lowering either the current density or the pH raises the zinc content of the deposit. Some baths have a levelling action, since bright deposits can be prepared from them on an etched surface. Examples of such baths are: (i) FeSO₄-7H₂O 248, ZnSO₄-7H₂O 8·8, (NHJ₄)₂SO₄ 118, KCl 10, citric acid 0·5 g./l., operated at pH 1·7, 50°G, 200 amps./ft.² and giving a 6% zinc alloy of 560 D.P.N, hardness;

(ii) FeSO₄-7H₂O 174, ZnSO₄-7H₂O 88, (NH₄)₂ SO₄ 118, KCl 10, citric acid 0·5 g., Teepol 0·4 ml./l., operated at pH 1·7, 50°C, 180 amps./ft.² and giving a 60% zinc alloy of 350 D.P.N, hardness.

The throwing power of the baths is comparable with that of a bright nickel bath. Pitting can be overcome by using a wetting agent (Teepol or Lubrol W) and operating at high temperature (80° C.) and low pH (<1·8). Under these conditions the deposits are usually matt and light grey in colour.

Alloys with zinc contents >ca. 30% have electrode potentials in N/10 KCl nearly equal to that of pure zinc. In the C.R.L. beaker test, the alloys with zinc contents between 30 and 90% are, in general, more corrosion resistant than pure zinc. Various applications of these alloys are proposed, including their use as an undercoat for paints and chromium plating and for decorative finishes indoors.

Deposition of iron-zinc alloys from chloride baths is dealt with briefly. A matt, corrosion-resistant alloy of 60% zinc content can be obtained, at pH 1·8, 50° C., and 50 amps./ft.², from a vigorously stirred bath of the following composition:—FeCl₂·4H₂O 177, ZnCl₂ 42, NH₄Cl 100, KCl 15, citric acid 0·5 g./l.

A colorimetrie method for the analysis of zinc in the presence of iron is described.     

Improved corrosion behavior of nanocrystalline zinc produced by pulse-current electrodeposition

Pulse electrodeposition was used to produce nanocrystalline (nc) zinc from zinc chloride electrolyte with polyacrylamide and thiourea as additives. Field emission scanning electron microscopy (FESEM) was used to study the grain size and surface morphology of the deposits and X-ray diffraction was used to examine their preferred orientation. Corrosion behavior of the electrodeposited nc zinc in comparison with electrogalvanized (EG) steel in de-aerated 0.5 N NaOH solution was studied using potentiodynamic polarization and impedance measurements. A scanning electron microscope (SEM) was used to characterize the surface morphology of the EG steel before corrosion testing. Surface morphologies of nc zinc deposits and EG steel were also studied after potentiondynamic polarization by SEM. Nanocrystalline zinc (56 nm) with random orientation was produced. The estimated corrosion rate of nc zinc was found to be about 60% lower than that of EG steel, 90 and 229 μA/cm², respectively. The surface morphology of corroded nc zinc was characterized by discrete etch pits, however, uniform corrosion was obtained after potentiodynamic polarization of EG steel. The passive film formed on the nc zinc surface seems to be a dominating factor for the corrosion behavior observed.     

The kinetics and mechanism of cathodic oxygen reduction on zinc and zinc–aluminium alloy galvanized coatings

A rotating disk electrode technique is used to investigate the kinetics and mechanism of O₂ reduction as it occurs at the surface of various hot-dip Al–Zn alloy coatings (on steel) immersed in weakly alkaline (pH 9.6) aqueous sodium chloride. The zinc component of coatings behaves electrochemically as though it were free zinc and the O₂ reduction pathway is determined by the potential dependent state of zinc. A 2e⁻ reduction to H₂O₂ predominates at potentials near the free corrosion potential, where zinc is (hydr)oxide covered. A 4e⁻ reduction to OH⁻ predominates at potentials where zinc is bare. Tafel slopes (∂E/∂log i) of 0.058 V dec⁻¹ and 0.132 V dec⁻¹ are determined for 2e⁻ and 4e⁻ O₂ reduction on pure zinc, respectively. Aluminium is virtually inert and varying aluminium content between 0.1% and 55% exerts little influence on O₂ reduction kinetics. However, all the Zn–Al alloy surfaces give very much higher O₂ reduction currents at low polarization than does pure zinc and it is proposed that this arises through an electrocatalysis of 2e⁻ O₂ reduction by traces of substrate derived iron.     

Effect of cations on corrosion of zinc and carbon steel covered with chloride deposits under atmospheric conditions

The effect of sodium, calcium, and magnesium chlorides deposited on zinc and carbon steel surfaces was studied under atmospheric conditions. The cations strongly affected the corrosion rate of zinc, whereas they had a significantly lower impact on the corrosion of carbon steel. The corrosivity of cations of chloride salts for zinc increased in order of Mg²⁺ < Ca²⁺ < Na⁺. The higher corrosion resistance of zinc treated with calcium and magnesium chlorides was connected to prevention of formation of hydrozincite during zinc exposure in wet air. It was observed that zinc weight loss and the carbonate to simonkolleite ratio in corrosion products were correlating. The principal protective effect of bivalent cations can be seen in the decrease of pH of the surface electrolyte, which was caused by hydrolysis of such cations and subsequent formation of simonkolleite that blocked the cathodic sites.     

Relation between microstructure and adhesion of hot dip galvanized zinc coatings on dual phase steel

The microstructure of hot dip galvanized zinc coatings on dual phase steel was investigated by electron microscopy and the coating adhesion characterized by tensile testing. The zinc coating consists of a zinc layer and columnar ζ-FeZn₁₃ particles on top of a thin inhibition layer adjacent to the steel substrate. The inhibition layer is a thin compact and continuous layer that consists of η-Fe₂Al_5–xZn_x fine and coarse particles. The coarse faceted particles are on top and fine faceted particles are at the bottom. The steel surface is covered with small fraction manganese oxides, which may impair adhesion of the zinc coating. The adhesion at various interfaces that exist in zinc-coated steel was quantitatively estimated using a so-called “macroscopic atom” model. In addition, the adhesion at the interfaces in zinc-coated steel was qualitatively assessed by examining the fracture and delamination behavior upon tensile testing. In accordance with this model, fracture along zinc grain boundaries preceded fracture along the zinc layer/inhibition layer and ζ-FeZn₁₃ particle/inhibition layer interfaces.     

Korrosionsverhalten feuerverzinkter Baustähle in überwiegend sandhaltigen Böden

Corrosion behaviour of galvanized steel in mainly sandy grounds In mainly sandy grounds with different portions of fine parts < 0,06 mm (2,5–20,4%) specimens of ungalvanized and galvanized steel were stored outside and in the laboratory. Besides the composition of the ground, the salinity and the temperature of the ground were varied too. The corrosion rate and, for ungalvanized specimens, the behaviour to pitting corrosion were determined. Furthermore the factors characterising the corrosion behaviour such as specific resistance of soil and corrosion potential were investigated continuously. The loss in weight of metal was much greater for ungalvanized than for galvanized specimens and increased for ungalvanized specimens with an increasing portion of fine parts in the ground. Additions of salt at the beginning of the tests produced an increased amount of metal wastage, but for galvanized specimens they only had an influence upon initial corrosion. The increased removals of material started since contents of 3 · 10^?3 MolCl^? + SO/kg. If salts were added to the ground after 2 years (after the formation of a surface layer), they increased the wastage of material for ungalvanized but not for galvanized specimens. Apart from ungalvanized bars in the soil with a fineness portion of 20,4%, corrosion, after an acceleration at the beginning, slowed down owing to the formation of a surface layer. Ungalvanized specimens were attacked by a strong pitting corrosion and that more in aerated than in dense and, thus, water-containing grounds. The additions of salt accelerate more an uniform corrosion of material than a pitting corrosion. As for galvanized specimens after a local removal of zinc under extreme conditions the steel base had been hardly corroded away. The parts free of zinc were protected cathodically by the still existing zinc. The corrosion of steel depends upon the temperature: by increasing the temperature from 4 to 20°C increases of corrosion up to 100% were stated. As for galvanized surfaces temperature has only a small influence upon corrosion.     

The alkaline stability of phosphate coatings I: ICP atomic emission spectroelectrochemistry

Inductively coupled plasma (ICP) spectroelectrochemistry was used to measure the alkaline resistance of zinc phosphate conversion layers on galvanized steel. The release of phosphate, zinc, manganese and nickel were measured quantitatively as a function of time when exposed to 0.1 M NaOH at ambient temperature. It was found that phosphate and zinc are removed in a 1:1 ratio during the early stages of the reaction so as to produce a residual hydroxide layer. The presence of Mn²⁺, Fe²⁺, or Ni²⁺ ions in the phosphate layer reduces the rate of phosphate leaching proportional to their degree of incorporation in the layer.