Typical Cr Research Articles

Characteristics and Applications of Sewage Sludge Biochar Modified by Ferrous Sulfate for Remediating Cr(VI)‐Contaminated Soils

Background. Soil contamination by hexavalent chromium is becoming a main environmental concern in China. This study developed a sewage sludge biochar modified by FeSO4 (CHBC) as a new reductant for Cr(VI)‐contaminated soil. The effectiveness of CHBC‐stabilized Cr(VI)‐contaminated soil was investigated. Methods. Typical industrial Cr(VI)‐contaminated soil in China was chosen as the medium. The total and Cr(VI) contents of the contaminated soil were 1014.6 and 973.5 mg/kg, respectively. The effectiveness of the Cr(VI)‐contaminated soil stabilized by CHBC was investigated by the leaching test (US EPA method 1312), the simplified bioaccessibility extraction test (US EPA 2007 protocol and British Geological Survey), alkaline digestion (US EPA method 3060A), sequential extraction (BCR sequential extraction procedure), X‐ray diffraction, and the risk assessment code test. Results. Results show that CHBC substantially reduced the leachability and Cr(VI) content of the contaminated soil. The leachability and content of Cr(VI) were lower than the thresholds of the Environmental Quality Standards of Soil in China for civil reuse and the China Environmental Quality Standards of surface water for civil use when the soil was stabilized with 10% dosage of CHBC. Conclusion. CHBC is highly efficient in stabilizing Cr(VI) and can effectively reduce the leachability and bioavailability of Cr in contaminated soil and thus feasible for stabilizing Cr(VI)‐contaminated soil and shows potential for application in the field.

Synthesis of Positively Charged Polystyrene Microspheres for the Removal of Congo Red, Phosphate, and Chromium(VI).

Uniform positively charged polystyrene microspheres were synthesized and further examined as a new sorbent for water remediation. The structures of the resulting sorbent were characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and 1H nuclear magnetic resonance spectroscopy. The adsorption performance of the sorbent was evaluated using three typical pollutants, namely, Congo red, phosphate, and Cr(VI). The adsorption isotherms were fitted by the Langmuir and Freundlich models, while the adsorption kinetics was analyzed by the pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations. The thermodynamic parameters of the adsorption process including changes of enthalpy, entropy and Gibbs free energy, and binding constant were obtained by isothermal titration calorimetry measurements. The effects of solution pH and competitive ions on the adsorption process were investigated. The adsorption isotherms could be better fitted by the Langmuir model, yielding maximum adsorption capacities of 18, 6.2, and 1.1 mg g–1 for the adsorption of Congo red, Cr(VI), and phosphate, respectively. The adsorption kinetics could be best described by the pseudo-second-order equation. The spent sorbent was regenerated by washing with 1 M KOH and showed outstanding long-term cyclic performance. The findings suggested that the positive charges at the surface of polystyrene microspheres could serve as effective sites for the immobilization of anionic pollutants in solutions owing to the electrostatic attraction.

Adsorption and reductive degradation of Cr(VI) and TCE by a simply synthesized zero valent iron magnetic biochar

To address inorganic and organic contaminants in the environment, economic new adsorbents are required. Here we test magnetic biochar for efficient capture of the typical pollutants Cr(VI) and trichloroethylene (TCE) from solution. We used a simple synthesis using 2M FeCl3 solution and peanut hull biomass to prepare magnetic ZVI biochar at alternate pyrolysis temperatures between 650 and 800 °C. The physicochemical character of the biochars were assessed using X-ray diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method for surface area. The magnetic ZVI biochars were highly effective in the removal of Cr(VI) and TCE. The most effective magnetic biochar produced at 800 °C was further examined using scanning electron microscopy (SEM), revealing a high and even loading of ZVI. After sorption the same magnetic biochar was examined by X-ray photoelectron spectroscopy (XPS) to ascertain the underlying mechanisms. The dependence of Cr(VI) capture on solution pH was also examined. Our interpretation suggests that when pH < pHzpc (2.5) electrostatic attraction and redox reactions dominated the adsorption of Cr(VI). When pH > pHzpc the removal process was controlled mainly by redox reaction and substitution of chromate anions for hydroxyl (OH) groups. Capture of TCE in contrast involved hydrophobic partitioning, pore-filling and reductive degradation. Overall our results suggest that simple synthesis of magnetic ZVI biochar could offer an economic and effective option to address water contamination issues.

Intense aqueous alteration on C-type asteroids: Perspectives from giant fine-grained micrometeorites

This study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of <1.2 in the scheme of Howard et al. (2015)) and reveal a range of alteration styles. Two particles are found to contain pseudomorphic chondrules with thick fine-grained rims, while another micrometeorite contains several aqueously altered CAIs. Their outlines range from well-defined to indistinct, demonstrating that the advanced stages of aqueous alteration progressively remove evidence of coarse-grained components. The remaining two micrometeorites entirely lack coarse-grained components but are similarly altered. Thus, the combined chondrule-to-matrix ratio among these giant micrometeorites is extremely low (6.45 area%), and significantly below the average ratio found in typical CM or CR chondrites (∼20%, Weisberg et al., 2006). Our findings are consistent with previous analyses from smaller Antarctic micrometeorites, which suggest that chondrules (and CAIs) derived from hydrated carbonaceous chondrite parent bodies are underrepresented among the micrometeorite flux, even when considering contributions from coarse-grained micrometeorites. Therefore, to explain the relative paucity of anhydrous material, we propose that the flux of fine-grained micrometeorites is primarily derived from intensely aqueously altered, primitive C-type asteroids, which have lost the majority of their refractory coarse-grained components by replacement with secondary phyllosilicate minerals.

Fate of Cr(III) during Ozonation of Secondary Municipal Wastewater Effluent

ABSTRACTIn the present study, the fate of trivalent chromium (Cr(III)) during ozonation of ultrapurified water and wastewater effluent was investigated. In experiments conducted in phosphate buffered ultrapurified water, O3 alone in excess was inefficient to oxidize Cr(III) (only about 10–15% of total Cr(III) content), while in presence of the secondary oxidant, OH radical, almost all Cr(III) was oxidized to hexavalent chromium (Cr(VI)). In a wastewater effluent, spiked with Cr(III), only about 10–20% of Cr(III) was oxidized with specific ozone doses in the range 0.15–1.5 gO3/gDOC, although O3 and OH radical were both available for reaction. Cr(VI) formation was monitored in parallel with the abatement of some common micropollutants, reacting with differing apparent second-order rate constants with ozone, decreasing in the order carbamazepine>> benzotriazole> atrazine> p-chlorobenzoic acid (pCBA). Carbamazepine and benzotriazole were abated to >80% for specific O3 doses of 0.3 gO3/gDOC and 0.8 gO3/gDOC, respectively. The more ozone-resistant compounds (atrazine and pCBA) required a specific ozone dose of about 1.25 gO3/gDOC for the same relative abatement. At this specific ozone dose (i.e., 1.25 gO3/gDOC), only about 20% of Cr(III) was oxidized to Cr(VI), whereas only 10% of Cr(III) was oxidized to Cr(VI) at a more realistic specific ozone dose for enhanced wastewater treatment for micropollutant abatement (0.5 gO3/gDOC). Therefore, for typical Cr(III) levels in municipal wastewaters, effluent ozonation only leads to toxicologically insignificant Cr(VI) concentrations.

Effect of alkaline precipitation on Cr species of Cr(III)-bearing complexes typically used in the tannery industry

Various organic compounds extensively used in the leather industry could influence the performance of alkaline precipitation with Cr(III). This study focused on two typical Cr(III)-bearing complexes (Cr(III)-collagen and Cr(III)-citrate) ubiquitous in tannery effluent yet with distinct treatment efficiencies, as Cr(III) was much more difficult to remove in the Cr(III)-citrate solution. Comprehensive analytical methods were employed to explore the intrinsic mechanism. It was found that a lower removal efficiency towards Cr(III) was significantly associated with higher oligomers. The molecular size of the Cr(III)-citrate complex continued to increase with rising pH, making it larger overall than Cr(III)-collagen species. The growing oligomer moiety of dissolved Cr(III)-complex species could persist in the stronger basic pH range, leading to the large amount of residual Cr(III) in the Cr(III)-citrate system. Combining this result with potentiometric titration and X-ray photoelectron spectroscopy data, it was believed that the polymeric species other than monomers facilitated resisting the attack from hydroxide ions, and the postulated Cr(III)-citrate species towards higher oligomers were discovered. Beyond that, both charge neutralization and sweeping effects were presented among the gradually emerging flocs in the Cr(III)-collagen system together with the electric double layer compression effect derived from salinity, thus resulting in a larger floc size and higher Cr(III) removal efficiency in saline solutions.

Zero-valent aluminum for reductive removal of aqueous pollutants over a wide pH range: Performance and mechanism especially at near-neutral pH

Zero-valent aluminum (ZVAl) draws much attention due to its strong reducibility. However, under neutral pH conditions, the reduction ability of ZVAl for pollutant removal has still been suspected because of the formed compact surface film of Al-(hydr)oxide. In this study, unmodified ZVAl was employed to reductively remove aqueous pollutants over a wide pH range, and its performance and mechanism, especially at near-neutral pH, were systematically studied for the first time. Results demonstrated that ZVAl had a wide range of pH applicability from 2 to 12, even in neutral environment. Typical nitro compound nitrobenzene (NB), typical azo dye acid orange 7 (AO7), and typical inorganic heavy metal ion Cr(VI) can be effectively removed at initial pH 7. Based on the changes of pH, ORP, DO, Al ions and TOC of the reaction solution, and the determination of reduction products of NB by UV–Vis and GC-MS, we found that NB removal by ZVAl can be primarily attributed to the reduction role. NB was reduced to nitrosobenzene firstly, and to aniline finally. Meanwhile, the adsorption phenomenon existed in this system. Next, the surface reaction mechanism was deeply revealed through the characterization of ZVAl particles before and after reaction by SEM-EDS, TEM, HRTEM, XRD, and XPS. It was found that ZVAl powders with core/shell structure participated in the redox reaction, and that ZVAl core was corroded, generating Al-(hydr)oxide. ZVAl surface oxide film was not directly removed, instead of a rougher one. Finally, the proposed reductive mechanism of aqueous pollutants by ZVAl was speculated from the angle of electronic competition. In water environment, O2, H2O and pollutants, with a clear competitive relationship, can capture electrons released from ZVAl. When pollutant's opportunities for getting electrons are enhanced, efficiently reductive reactions for pollutant removal can take place, even at near-neutral pH. In a word, ZVAl is a promising material to remove aqueous pollutants over a wide pH range, even in neutral environment, which exhibits its great potential as an effective and environment-friendly agent for pollutant removal from water.

Accumulation of heavy metals in soil-crop systems: a review for wheat and corn.

The health risks arising from heavy metal pollution (HMP) in agricultural soils have attracted global attention, and research on the accumulation of heavy metals in soil-plant systems is the basis for human health risk assessments. This review studied the accumulation of seven typical heavy metals-Cd, Cr, As, Pb, Hg, Cu, and Zn-in soil-corn and soil-wheat systems. The findings indicated that, in general, wheat was more likely to accumulate heavy metals than corn. Bioconcentration factor (BCF) of the seven heavy metals in wheat and corn grains decreased exponentially with their average concentrations in soil. The seven heavy metals were ranked as follows, in ascending order of accumulation in corn grains: Pb < Cr < Zn < As < Cu < Cd <Hg. As for the order of accumulation in wheat grains, their ranking was as follows: Zn < Pb < Cr < Cu < As < Hg <Cd. The minimum BCFs of Cd, Cr, As, Pb, Hg, Cu, and Zn in corn grains were 0.054, 6.65×10-4, 7.94×10-4, 0.0044, 0.028, 0.13, and 0.19, respectively. The corresponding BCFs values for wheat grains were 0.25, 0.0045, 5.42×10-4, 0.009, 4.03×10-4, 0.11, and 0.054, respectively.

Chromium Extraction via Chemical Processing of Fe-Cr Alloys Fine Powder with High Carbon Content

Ferrous alloys are important raw materials for special steel production. In this context, alloys from the Fe-Cr system, with typical Cr weight fraction ranging from 0.45 to 0.95, are prominent, particularly for the stainless steel industry. During the process in which these alloys are obtained, there is considerable production of fine powder, which could be reused after suitable chemical treatment, for example, through coupling pyrometallurgical and hydrometallurgical processes. In the present study, the extraction of chromium from fine powder generated during the production of a Fe-Cr alloy with high C content was investigated. Roasting reactions were performed at 1073 K, 1173 K, and 1273 K (800 °C, 900 °C, and 1000 °C) with 300 pct (w/w) excess NaOH in an oxidizing atmosphere (air), followed by solubilization in deionized water, selective precipitation, and subsequent calcination at 1173 K (900 °C) in order to convert the obtained chromium hydroxide to Cr2O3. The maximum achieved Cr recovery was around 86 pct, suggesting that the proposed chemical route was satisfactory regarding the extraction of the chromium initially present. Moreover, after X-ray diffraction analysis, the final produced oxide has proven to be pure Cr2O3 with a mean crystallite size of 200 nm.

Bi25VO40 microcube with step surface for visible light photocatalytic reduction of Cr(VI): Enhanced activity and ultrasound assisted regeneration

In this study, a kind of bismuth vanadium (Bi25VO40) microcube with step surface was successfully synthesized by a fast and mild hydrothermal method. The reaction time and hydrothermal temperature are the key factors which are accounted for the formation of this unique structure. The as-prepared Bi25VO40 microcube exhibited considerably higher visible light photocatalytic activity compared with the smooth one, revealing that fabrication of Bi25VO40 with step surface was an effective method to improve the photocatalytic activity. The enhanced photocatalytic activity over this Bi25VO40 could be attributed to its enhanced separation efficiency of photo-generated holes and electrons. In addition, the XPS analysis of the Bi25VO40 after photo-reduction showed that most of highly toxic Cr(VI) were reduced into less dangerous Cr(III). The XRD results indicated the reduced Cr(III) existed in the form of Cr2O3 and Cr3O8 on the catalyst surface and occupied the active site, counting for the decreased activity after multiple use. A facile ultrasound treatment facilitated the regeneration of deactivated photocatalyst by removing the adsorbed Cr2O3 and Cr3O8, improving the removal ratio of Cr(VI) over the photocatalyst from 74.0% to 85.6% after four recycling use, which make it applicable for the photocatalytic removal of a typical Cr(VI) pollutant continuously.

Site occupancy behaviours of ternary elements (Zr, Mo, Cr) in the Laves phase of C15 NbCo2: a first-principles study

First-principles method based upon the density functional theory has been carried out to investigate the site occupancy behaviours of typical ternary elements Zr, Cr and Mo in the C15 NbCo2 Laves phase. The calculated equilibrium lattice constant of the Nb8Co16 unit cell is in good agreement with the previous experimental results. The calculated results indicate that all the considered ternary elements show the preference to occupy the Co sites, and the site preference of these elements in the Laves phase is in the order of Cr, Mo and Zr. Mo and Cr atoms tend to participate in the formation of the Laves phase, generating Nb7MoCo16, Nb8Co15Mo and Nb8Co15Cr, respectively. Zr atoms are not prone to concentrate in the Laves phase. The partial density of states was also calculated to investigate how atoms interact, and the charge density difference is analysed to reflect the bonding characteristics.

A favorable chromium coating electrodeposited from Cr(III) electrolyte reveals anti-wear performance similar to conventional hard chromium

Decades of application has proved that electrodeposited chromium (Cr) coating is a perfect coating material. Unfortunately, almost all of these excellent coatings for anti-wear, i.e., hard Cr coatings, are produced by traditional electrodepositing process based on highly toxic Cr(VI). In this research, we reported a promising Cr coating embedded with graphite nanocrystals, which was electrodeposited from a Cr(III) electrolyte and reveals favorable anti-wear performance similar to that of conventional hard Cr coating in a range of sliding velocities. In addition, the developing direction of researches on electrodepositing thick Cr coating from Cr(III) electrolyte was elucidated via comparative investigation of the friction and wear behaviors of three typical Cr coatings.

Nitrogen-doped bcc-Cr films: Combining ceramic hardness with metallic toughness and conductivity

We report the first results on nanostructured N-doped bcc-Cr films exhibiting the unique combination of ceramic hardness with metallic toughness and electrical conductivity at unexpectedly low N concentrations, ~5at.%. The Cr:N films are deposited at 200°C in N2/Ar mixtures by high-power pulsed magnetron sputtering using tunable time-domain control of Cr+ and Cr2+ ion fluxes incident at the film growth surface. Subplanted N atoms impede annealing of metal-ion induced point defects and hinder bcc-Cr grain growth, resulting in a material with a nearly isotropic nanostructure and atomically smooth surface, rather than typical Cr:N solid solutions consisting of faceted microcolumns.

INFLUENCE OF POLLUTION BY HEAVY METALS ON BIOLOGICAL PROPERTIES OF MOUNTAIN CHERNOZEMS OF THE SOUTH OF RUSSIA

Pollution of the chernozem typical (mountain) Cr, Cu, Ni and Pb oxides leads to deterioration of its condition: activity of a catalase and dehydrogenase decreases, cellulolytic activity, an abundance of bacteria of the sort Azotobacter, worsen indicators of germination and initial growth of a garden radish. Extent of decrease depends by nature metal and its concentration in the soil. The studied TM oxides form the following row on extent of negative impact on biological properties of the chernozem of typical (mountain): CrO3> CuO> = PbO> = NiO.

Efficient removal of a typical dye and Cr(vi) reduction using N-doped magnetic porous carbon

Download options Please wait... Supplementary files Supplementary movie MP4 (2791K) Supplementary information PDF (1138K) Article information DOI https://doi.org/10.1039/C4RA10189H Article type Paper Submitted 11 Sep 2014 Accepted 03 Nov 2014 First published 04 Nov 2014 Download Citation RSC Adv., 2014,4, 63110-63117 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Efficient removal of a typical dye and Cr(VI) reduction using N-doped magnetic porous carbon S. Zhang, X. Wang, J. Li, T. Wen, J. Xu and X. Wang, RSC Adv., 2014, 4, 63110 DOI: 10.1039/C4RA10189H To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Shouwei Zhang Xiangxue Wang Jiaxing Li Tao Wen Jinzhang Xu Xiangke Wang

Metals as electron acceptors in single-chamber microbial fuel cells

Two typical oxidized-status metals (Fe(III) and Cr(VI)) were studied as electron acceptors on cathodes in single chamber microbial fuel cells (SCMFCs) to explore novel sustainable technology for metal treatment. The batch-mode tests indicated that the voltages of SCMFCs steadily increased with Fe(III) concentrations (10, 30, and 50 mg L−1) and Cr(VI) concentrations (1, 3, and 10 mg L−1). The maximum power density was 658 ± 6 mW m−2 at 50 mg L−1 of Fe(III), and 419 ± 4 mW m−2 at 10 mg L−1 Cr(VI). The conversion efficiency of Cr(VI) and Fe(III) were high (>89%), and coulombic efficiency ranged 23–100%. Cr(VI) concentration of 10 mg L−1 started to irreversibly inhibit SCMFCs. The open circuit potentials (OCPs) well reflected the organic substrate removal in anode and metal reduction on cathode. Cathode liner sweep voltammetry (LSV) showed the electrochemical activity increased with metal concentrations, and the cathode of Fe(III) had better LSV performance than Cr(VI). Microbial community analysis of biofilms showed that the DNA band patterns of anode biofilms were similar, while cathode biofilms varied with electron acceptors. This study demonstrated the high power generation of SCMFCs with metals as electron acceptors, and revealed the great potential of expanding MFCs for diverse waste treatment.

LIBS Detection of Heavy Metal Elements in Liquid Solutions by Using Wood Pellet as Sample Matrix

Laser-induced breakdown spectroscopy (LIBS) has been applied to the analysis of heavy metals in liquid samples. A new approach was presented to lower the limit of detection (LOD) and minimize the sample matrix effects, in which dried wood pellets absorbed the given amounts of Cr standard solutions and then were baked because they have stronger and rapid absorption properties for liquid samples as well as simple elemental compositions. In this work, we have taken a typical heavy metal Cr element as an example, and investigated the spectral feasibility of Cr solutions and dried wood pellets before and after absorbing Cr solutions at the same experimental conditions. The results were demonstrated to successfully produce a superior analytical response for heavy metal elements by using wood pellet as sample matrix according to the obtained LOD of 0.07 ppm for Cr element in solutions.

A XAFS study of plain and composite iron(III) and chromium(III) hydroxides

Reduction of hexavalent Cr(VI) to the trivalent state is the common strategy for remediation of Cr(VI) contaminated waters and soils. In the presence of Fe the resulting compounds are usually mixed Fe(III)–Cr(III) phases, while, under iron-free conditions, reduction leads to formation of plain Cr(III) hydroxides. Environmental stability of these compounds depends on their structure and is important to understand how different precipitation conditions affect the local atomic order of resulting compounds and thus their long term stability.In current study, typical Cr(VI) environmental remediation products, i.e. plain and mixed Fe(III)–Cr(III) hydroxides, were synthesized by hydrolysis and redox reactions and their structure was studied by X ray diffraction and X ray absorption fine structure techniques. Plain Cr(III) hydroxide was found to correspond to the molecular formula Cr(OH)3·3H2O and was identified as crystalline in XRD. However, the same compound when examined by EXAFS did not exhibit any clear local order in the range of EXAFS detectable distances, i.e. between 0 and 5Å. Namely, EXAFS spectroscopy detected only contribution from the first nearest neighboring (Cr–O) shell, suggesting that CrO6 octahedra interconnection is loose, in accordance with the suggested anti-bayerite structure of this compound.Mixed Fe(III)–Cr(III) systems resembled 2-line ferrihydrite irrespective of the synthesis route. Analysis of Fe-K-EXAFS and Cr-K-EXAFS spectra indicated that FeO6 octahedra are bonded by sharing both edges and corners, while CrO6 octahedra seem to prefer edge sharing linkage. EXAFS data also suggest that Fe–Cr hydroxide produced by hydrolysis presents a better arrangement of CrO6 octahedra compared to the redox product.

Investigation of Cr(VI) reduction and Cr(III) immobilization mechanism by planktonic cells and biofilms of Bacillus subtilis ATCC-6633

In this study, we investigated the Cr(VI) uptake mechanism of planktonic cells and biofilms of Bacillus subtilis (B. subtilis) ATCC-6633. Data showed that the effect of planktonic cells on the Cr(VI) uptake was quite different from that of biofilms. Planktonic cells had strong ability of Cr(VI) reduction, while biofilms possessed a great potential of Cr(III) immobilization. For planktonic cells, 100 mg/L Cr(VI) could be completely reduced. Both exopolymeric substances and cytoplasmic extracts contributed to high capacity of Cr(VI) reduction. After the reduction, noticeable Cr(III) precipitates were accumulated on bacterial surfaces, but 37.5% Cr(III) still remained in the supernatant. For biofilms, the biofilm debris became the main active ingredient of the Cr(VI) reduction. However, only 20 mg/L Cr(VI) could be reduced probably because of unavailability of reducing active sites during the biofilm formation. Further studies showed that biofilms had a better Cr(III) immobilization capacity than planktonic cells with 100% Cr(III) immobilized. Moreover, for the first time, we proposed a strategy combining the advantages of both planktonic cells and biofilms, and a successful Cr(VI) removal from typical Cr(VI)-containing plating wastewater was achieved through a 10-L pilot-scale experiment.

Interaction of La0.58Sr0.40Co0.20Fe0.80O3−δ cathode with volatile Cr in a stack test – Scanning electron microscopy and transmission electron microscopy investigations

Anode-supported solid oxide fuel cells with special thin-film yttria-stabilized zirconia electrolytes made by sol–gel technology were operated in a short stack sequentially for about 1300 h at temperatures of 700 °C and subsequently for 1200 h at 600 °C, respectively. The stack was operated galvanostatically at a constant current density of 500 mA cm−2. After operation, the stack was dismantled and the cells were analyzed with respect to Cr interaction with the LSCF cathode. Chemical analysis revealed typical overall Cr amounts of several tenths μg cm−2 cathode area depending on the operation time. SEM cross sections showed less SrCrO4 formation at the typical sites for LSCF (top side of cathode) but there was evidence of chromate formation at the border between the cathode and barrier (electrolyte) layer. This location of foreign phase formation was unexpected. Additional TEM characterizations were therefore conducted. The TEM investigation verified the presence of Cr-containing crystals and revealed pore formation in the barrier layer. The formation of SrCrO4 at this borderline and pore formation were found for the first time after SOFC stack operation.