Strontium Chromate Research Articles

Specific features of the corrosion inhibition of an aluminum alloy by a nonchromate pigment mixture

The combination of zinc phosphate/molybdate and calcium-containing ion-exchange pigment enables one to inhibit efficiently the local corrosion of an aluminum-copper alloy in a slightly acid medium. Here, the charge-transfer resistance of the metal under the action of extract of this mixture of nonchromate pigments is at the same level as in a medium with the extract of strontium chromate. Using the methods of surface analysis, we have established that this protective effect is caused by the deposition of a protective film on the aluminum matrix (anode) and intermetallic phase (cathode). Under the corrosion potential, a protective film, consisting of a mixture of zinc and calcium phosphates with admixture of zinc hydroxide, is formed on a specimen of the alloy in a medium inhibited by a nonchromate mixture. Mainly zinc phosphate and zinc hydroxide with admixture of calcium phosphate deposit on the cathode polarized surface of the alloy under study. Under anodic potentials, the film consists of zinc and aluminum phosphates.

One-step synthesis of lamellar molybdate pillared hydrotalcite and its application for AZ31 Mg alloy protection

A novel anticorrosion pigment for AZ31 Mg alloy protection, molybdate pillared hydrotalcite (HT-MoO 4 2−), was successfully fabricated via a simple one-step process. The physicochemical properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectra, and inductively coupled plasma (ICP) method, respectively. The results indicated that the material showed typical characteristics of molybdate intercalated hydrotalcite. Additionally, it was found that the sample exhibited nano-sized lamellar morphology with the particle size of 35–60 nm. Moreover, the coating on AZ31 Mg alloy containing HT-MoO 4 2 − pigment showed obviously higher corrosion protection performance in comparison with the strontium chromate (SC) pigment by Electrochemical impedance spectroscopy (EIS) measurements. The mechanism of corrosion protection was proposed to be that the HT-MoO 4 2 − pigment in the coating would cause the pigment to undergo amphoteric ion exchange with aggressive NaCl solution, leading to the release of molybdate and Zn 2+ inhibitors.

Corrosion protection of magnesium alloy ZM21 by polyaniline-blended coatings

Phosphate-doped polyaniline pigment was prepared by a chemical oxidation method using ammonium persulfate in phosphoric acid media. Fourier transform infrared studies were done to characterize the pigment. The magnesium alloy ZM 21 was coated with polyaniline-pigmented paint, based on an epoxy binder, and the corrosion performance of the coating was studied by potential measurements and electrochemical impedance spectroscopy in 0.1% and 0.5% NaCl solutions. The results were compared with strontium chromate and filler material-pigmented coatings. It was found that the coating containing polyaniline provided similar protection for the magnesium alloy as that offered by chromate-pigmented paint.

Chemical Stability of Ferritic Alloy Interconnect for SOFCs

A ferritic alloy interconnect was studied through solid oxide fuel cell (SOFC) stack operation at intermediate temperatures. Certain pretreatment of the alloy surface proved to be effective for controlling initial degradation of the stack performance, presumably by the formation of stable and conductive oxide scale. Evidences were found that glass sealant containing alkali metals affected the oxidation behavior of the alloy surface not in contact with the cathode material. A thick scale rich in iron tended to be formed at the air side in the vicinity of the glass sealant, while a thinner scale rich in chromium was preferably found in the other. Alkali metal components were found in that thick oxide layer. At the interface between the alloy and the cathode current collector, a strontium chromate, which might cause chromium poisoning at the cathode/electrolyte interface, was formed, and that was found to be distributed over the current collector away from the interface. A thermodynamic equilibrium calculation using a thermodynamic database revealed that the chromium component is highly reactive with alkali or alkali earth metals and forms stable chromates. Some of those chromates are very stable and may hinder the formation of stable oxide scale such as spinels or , and may cause the severe oxidation of the alloy.

Corrosion protection of aluminum alloys by inhibiting pigments

We show that calcium monohydrophosphate can serve as an efficient inhibiting component of anticorrosive coatings applied on an aluminum-copper alloy. It has been established that the charge-transfer resistance of D16T alloy under the influence of CaHPO4 solution approaches the value characteristic of a medium with strontium chromate. Calcium monohydrophosphate simulates the behavior of strontium chromate inhibitor, retarding the cathodic and anodic corrosion reactions on the surface of aluminum alloys.

Chrome free pigments for corrosion protection in coil coated galvanised steels

A range of bentonite clays such as Wyoming (W), hybond (H), cat litter (CL) and versions exchanged with Ce3+, Y3+, La3+ and Ca2+ cations used as the corrosion inhibitors in the 5 μm polyester primer layer applied to 0·7 mm gauge hot dip zinc (0·15%Al) galvanised steel materials, over coated with a 20 μm architectural polyester coating. Similar primer systems have been prepared containing strontium chromate (Cr), Shieldex (Shd) and titanium dioxide (TiO2) for the purposes of comparison. The scanning vibrating electrode technique (SVET) was used to probe the corrosion kinetics at sample cut edges immersed in 5%NaCl on a limited number of the coatings based on the Wyoming bentonite. The SVET determined zinc losses for the pigments tested over 24 h were as follows: Shd (920 μg), Cr (740 μg), W–Y (655 μg), W–Ce (560 μg), W (550 μg) and W–Ca (496 μg). The same samples together with all of the other pigmented coatings were also subjected to salt spray testing. The average maximum cut edge corrosion delamination distances were: Cr (14 mm), Shd (20 mm), TiO2 (100 mm), W (13 mm), H (17 mm), CL (14 mm), W–Ca (10 mm), H–Ca (15 mm) W–Ce (9 mm), H–Ce (10 mm), W–Y (13 mm) and H–Y (15 mm). The performance trends over 1000 h of salt spray testing were in broad agreement with the 24 h SVET data for those samples tested in both ways. The ion exchanged and naturally occurring bentonites appear to be promising corrosion inhibitors for coated galvanised steel. In order to maximise performance, a fully formulated system has been developed on a 4·5Al–95·5Zn galvanised substrate which has a PVC plastisol top coat. A bentonite matrix with higher ion exchange capacity (>1 mequiv g−1) and low silica content has been developed (IM–X, where X is Ce3+, Ca2+ or Zn2+). In this system delamination distances have been reduced to extremely low levels of IM–Ce 0·3 mm, IM–Ca 0·45 mm and IM-Zn 0·37 mm.

Comparison of the efficiency of inorganic nonmetal pigments with zinc powder in anticorrosion paints

This paper deals with the study of properties of anticorrosion pigments of varying chemical composition in epoxyester paints. Two type lines of paints were prepared. The first line comprised an anticorrosion pigment with a PVC concentration of 10% while the other line comprised an anticorrosion pigment with a PVC concentration = CPVC. The following nontoxic anticorrosion pigments were observed: zinc phosphate, zinc phosphomolybdate, calcium hydrogen phosphate, zinc phosphate modified with an organic corrosion inhibitor, strontium–aluminum polyphosphosilicate, zinc–aluminum polyphosphate, calcium metaborate, calcium ferrite, calcium borosolicate, and strontium chromate. The epoxyester primers were observed for the effect of the type of pigment on the anticorrosion properties. Anticorrosion efficiency was derived from tests in a condenser chamber and in a salt spray cabinet as well as from a test of chemical resistance of pigmented coatings. The evaluation of anticorrosion efficiency of inorganic nonmetal pigments was carried out by means of comparison with anticorrosion efficiency of metal dust.

Shiny Science: A New Substitute for Hexavalent Chromium

Although perhaps more familiar to those of us of a certain age who remember when all cars had sparkling mirror-finish bumpers, chromium still plays a big part in industry. Chromium is valued for its brightness, durability, resistance to corrosion, and hardness. It is used as a pigment in paint, inks, and plastics, as an anticorrosion agent in protective coatings, and in chrome plating on such things as aircraft engine components, tool and die parts, railroad wheel bearings, and, of course, the “brightwork” that trims motorcycles, cars, and trucks. As more and more scientific studies have revealed, however, chromium also has a darker side. The chromium used in the plating industry is primarily hexavalent chromium, which is a very different animal from the trivalent form required by the human body. Hexavalent chromium is a potent human carcinogen, and can also cause dermal irritation and kidney and liver damage. Now, in an effort to find safer alternatives, researchers are looking at tailored nanostructures that offer the appearance and durability of hexavalent chromium without the hazards.

Cut Edge Corrosion Protection in Organically Coated Galvanized Steels Using Ion Exchanged and Naturally Occurring Clay Mineral Pigments

Two bentonite clays Wyoming-(W), Hybond-(H) and versions exchanged with Ce3+, Y3+, La3+ and Ca2+ cations were used as the corrosion inhibitors in the 5μm polyester primer layer on 0.7mm galvanized steel materials coated with a 20μm architectural polyester. Similar primer systems have been prepared containing Strontium Chromate-(Cr), ShieldexTM-(Shd) and Titanium Dioxide-(TiO2). The scanning vibrating electrode technique was used to investigate cut edge corrosion in 5% NaCl. The zinc losses over 24 hours were as follows: Shd (920 μg), Cr (740 μg), W-Y (655 μg), W-Ce (560 μg), W(550 μg) and W-Ca (496 μg). Samples were also subject to salt spray testing and there was good agreement between the SVET and salt spray data. The average maximum cut edge corrosion delamination distances were Cr (14mm), Shd (20mm), TiO2 (100mm), W (13mm), H (17mm), WCa (10mm), HCa (15mm), WCe (9mm), HCe (10mm), WY (13mm) and HY (15mm).

Effects of Chrome Contamination on the Performance of La0.6Sr0.4Co0.2Fe0.8O3 Cathode Used in Solid Oxide Fuel Cells

Chrome poisoning effects of various Cr-containing metal sources on the electrochemical performance of the (LSCF6428) cathode have been investigated. It was found that chromia-forming metals caused significant fade in power density due to the chrome poisoning, while alumina-forming alloys exhibited no influence on the cell degradation. This degradation caused by the chrome poisoning was accelerated at higher operating temperatures. Microstructural analysis conducted on the cells tested with chromia formers exhibited the formation of a strontium chromate phase in the entire cathode, leading to the homogeneous distribution of Cr in the cathode. Although the Mn-containing chromia former such as Crofer22 formed a continuous layer of the oxide scale on the mesh surface, it was not effective enough to prevent Cr poisoning of the cathode. In contrast, alumina formers such as Haynes214 and Kanthal formed a continuous layer of the alumina scale, resulting in no Cr contamination in the LSCF6428 cathode.

Large-scale Synthesis of SrCrO4 Nanowires and PbCrO4 Nanorods by a Solution-phase Method at Room Temperature

Abstract A facile, large-scale, solution-phase method has been developed to the synthesis of ABO4-type chromate nanowires/rods at room temperature. Single-crystalline strontium chromate nanowires and lead chromate nanorods were fabricated by this method without heating or adding any surfactants or polymers. The structure and morphology of the nanowires/rods were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and selected-area electron diffraction (SAED). This simple method may also be extended to the synthesis of other ABO4-type chromate one-dimensional nanostructures with a large-scale and low-cost production.

SNCZ sees no decline in market for strontium chromate corrosion inhibitor

SNCZ sees no decline in market for strontium chromate corrosion inhibitor

Inhibition of mild steel by strontium chromate in artificial acid rain solution

The inhibition of mild steel in an artificial acid rain solution (pH 4·5) in low concentrations of strontium chromate pigment has been evaluated using a range of methods: potentiodynamic polarisation, electrochemical impedance, X-ray photoelectron spectroscopy and solution analysis. The individual effects of strontium and chromate have been evaluated and have been used to estimate inhibitor efficiency and film composition, and to determine the possible inhibition mechanism. The results show that, at low concentration, strontium chromate affects the cathodic reaction, with reduction of Cr6+ to Cr3+, and the surface film was composed of magnetite and hydrated chromium hydroxide. The presence of strontium was not found significantly to affect the inhibitory performance.

Microscopic analysis of the chromium content in the chromium-induced malignant and premalignant bronchial lesions of the rat

Objective: Our previous studies demonstrated that the frequency of gene instability in lung cancer of chromate workers was very high, but the frequencies of the p53 and ras gene mutations were low. To clarify the carcinogenesis of chromate in the lung, we established a chromate-induced cancer model in the rat proximal airway and examined the relationship between chromium accumulations and the chromium-induced cancer and premalignant bronchial lesions of the rat. Methods: Fifteen male, bred, 12-week-old Jcl-Wister rats were used. A pellet of strontium chromate were inserted into the bronchus of the rats. The rats were sacrificed 9 months after the pellet was inserted. We pathologically examined the region of the bronchi to which the pellet was attached. We quantified the amount of chromium accumulation in the bronchial lesions using a microscopic X-ray fluorescence analyzer. Results: Of the 15 rats, 1 rat had a lesion of squamous cell carcinoma (SCC), 7 rats had carcinoma in situ (CIS) or dysplasia, 8 rats had squamous metaplasia, and 5 rats had goblet cell hyperplasia. The amounts of chromium accumulation in normal epithelium ( n = 24 ), goblet cell hyperplasia ( n = 14 ), squamous metaplasia ( n = 8 ), and dysplasia plus CIS plus SCC ( n = 9 ) were 500±1354, 713±1062, 941±1328, and 3511±4473 (mean±SD) counts/s/mA, respectively. The amount of chromium accumulation was significantly increased according to the progression of malignant change of the bronchial epithelium (Spearman's correlation coefficient by ranks, rs = 0.454 , P < 0.01 ). Conclusions: The amount of chromium accumulation was significantly increased according to the progression of malignant change of the bronchial epithelium. Examining the genetic alterations of histologic changes in this model was helpful in elucidating the process of carcinogenesis of chromium in the lung.

Size Distribution and Speciation of Chromium in Paint Spray Aerosol at an Aerospace Facility

Spray painters are potentially exposed to aerosol containing Cr(VI) via inhalation of chromate-based paint spray. Two field studies were conducted at an aerospace facility to determine the size distribution and speciation of Cr(VI) in paint spray aerosol. Sampled paint products consisted of sparingly soluble strontium chromate in an epoxy resin matrix, a matrix generally known for its durability and toughness. Personal aerosol samples were collected using Sierra Marple personal cascade impactors and analyzed for Cr(VI) and total Cr. The size distribution of total Cr particles in the paint aerosol had a Mass Median Aerodynamic Diameter (MMAD) of 7.5 mum [Geometric Standard Deviation (GSD = 2.7 mum)] in both field studies. The MMAD of Cr(VI) particles was 8.5 mum (GSD = 2.2 mum). Particles >2 mum constituted 90% or more of the total Cr and the Cr(VI) mass, in all sampled paint aerosols and were lognormally distributed. The target site for respiratory deposition of Cr in the aerosol was estimated based on the mass distribution of Cr according to particle size. On an average, 62% of the Cr and Cr(VI) mass in the paint aerosol consisted of particles >10 mum. This study showed that 71.8% of Cr(VI) mass in paint spray aerosol potentially inhaled by a spray painter may deposit in the head airways region. Only 2.0 and 1.4% of Cr(VI) mass in the paint aerosol may potentially deposit in the alveolar and tracheobronchial region, respectively. The ratio of Cr(VI) mass to total Cr mass was determined in bulk paint and the data indicate that Cr was predominantly in the Cr(VI) valence state, before spraying. The ratio of Cr(VI) mass to total Cr mass was also determined in paint aerosol samples. The data indicated that there was a reduction of Cr(VI) regardless of Cr aerosol particle size. Cr(VI) reduction occurred most likely during the 8 h sample collection time period. These findings are in agreement with the findings that observed Cr(VI) reduction during collection of airborne Cr(VI) in samples of chromic acid mist. The use of Cr(VI) stabilizing sampling media and the storage of samples at lower temperatures (4 degrees C ) during and after sampling may avoid the underestimation of Cr(VI).

Protective Action of Phosphate and Calcium-Containing Pigments under the Conditions of the Stress Corrosion Fracture of Steels

We have established that strontium chromate and a mixture of modified zinc phosphate and calcium-containing pigment inhibit substantially the corrosion of low-carbon steel in slightly acid rain solution. We observed mainly the anodic control of corrosion in the extract of chromate pigment and mixed control in the extract of a mixture of nonchromate pigments. Zinc ions in corrosive media enhance significantly the protective action of this pigment mixture. Here, a crystal-like protective film, consisting of calcium and zinc phosphates, is formed on the surface of steel. The extracts of chromate pigment and a mixture of nonchromate pigments in a slightly acid medium increase the resistance of low-carbon steel to corrosion fatigue in the stages of crack initiation and growth. Thus, the necessary prerequisites are created for enhancing the service life of steel constructions with organic coatings, containing inhibiting pigments, under conditions of the joint action of a corrosive medium and cyclic loading.

Chromate Inhibition of Filiform Corrosion on Organic Coated AA2024-T3 Studied Using the Scanning Kelvin Probe

The influence of in-coating strontium chromate pigment dispersions on the kinetics and mechanism of HCl-induced filiform corrosion (FFC) affecting polyvinyl butyral coated AA2024 T3 aluminum alloy is studied using a scanning Kelvin probe. FFC initiation and propagation are detected by imaging time-dependent changes in local free corrosion potential distribution patterns. Area rates of coating delamination fall from to zero as the volume fraction is increased from zero to 0.06. Increasing over the same range produces minimal change in filament-head values but depresses filament tail and intact coating values by up to 0.3 V. It is proposed that filament tail depression results from increased polarization of cathodic reduction reactions at sites of high pH, where insoluble is the predominant reduction product. It is further proposed that intact coating depression results from reversible, nonfaradaic adsorption of at the oxide-covered aluminum surface. Both effects are implicated in FFC inhibition, as is pH buffering by which acts in conjunction with adsorption to forestall anodic attack at the coating-substrate interface. © 2004 The Electrochemical Society. All rights reserved.

The effect of strontium and chromate ions on the inhibition of zinc

The corrosion and inhibition of zinc in artificial acid rain solution (pH 4.5) at a low strontium chromate concentration has been evaluated using electrochemistry, solution analysis and XPS. These techniques have been used to estimate inhibitor efficiency and to determine a possible inhibition mechanism. The results show that strontium chromate at low concentration inhibited significantly more of the cathodic corrosion process, by reduction of Cr 6+ to a solid species containing Cr 3+. The surface film contained a mixture of oxidised zinc and chromium, probably in the form of basic zinc carbonate (hydrozincite) and hydrated chromia. Importantly strontium ions were found to play no significant role in the inhibition process.

A model for the release of chromate from organic coatings

The kinetics of chromate release from a polyester isocyanate has been studied as a model of the inhibitor transport from organic coatings, which is essential for corrosion protection of bare metals at scribes and cut-edges. The primer was pigmented with strontium chromate and applied on hot-dip galvanized steel. The influence of temperature from 3 to 60 °C, pH and chloride concentration in the leaching solution on the dissolution kinetics and total amount of chromate released during 15 days of exposure was determined. The results were compared with four commercial line-coated primers. The rate of release of chromate from the polyester coating into water solutions showed a logarithmic dependence with time with an apparent break connected to the diffusion of the leaching solution through the coating. Comparatively very high amount of chromate was released during the first minutes of the exposure, being almost immediately available for the corrosion inhibition. The highest amount of chromate released during the first 15 days of exposure was found at 20 °C; both an increase and decrease of temperature lowered the rate of chromate release. The effect of temperature was likely due to a modification of the strontium chromate particle/organic matrix interface in the presence of water in the coating structure. The acidic environment, typical for defects in organic coatings, increased the chromate dissolution in comparison with neutral solutions. Diffusion of water and chromate solution through the investigated polyester primer played an important role in chromate release, especially at the beginning of the process. However, the rate-controlling step of the leaching was very probably related to the chromate release at the pigment particle and coating matrix interface.

Durability of an off-optimum cured aluminium joint

The durability of an aluminium alloy joint, in which the adherends have been pre-treated with silane coupling agent and strontium chromate primer and bonded with the film adhesive FM-73, was examined for an off-optimum adhesive cure cycle. For bonded repairs a cure cycle of low temperature and longer duration (8 h at 80°C) for FM-73 is employed regularly to reduce thermal stresses. Double cantilever beam testing showed that the improved durability that results from primer application when the adhesive is cured at 120°C does not occur for the 80°C cure. Scanning electron microscopy and X-ray photoelectron spectroscopy of fracture surfaces and cross-sections cut from test specimens indicate differences in fracture paths and interfacial regions for the 120°C and 80°C cure specimens. Changes in the interphase region caused by the off-optimum cure cycle may contribute to an increased susceptibility of the adhesive joint to moisture and consequent bond degradation.