In this work, the combination of biological and electrochemical processes to mineralize oxyfluorfen has been studied. First, an acclimatized mixed-culture biological treatment was used to degrade the ...biodegradable fraction of the pesticide, reaching up to 90% removal. After that, the non-biodegraded fraction was oxidised by electrolysis using boron-doped diamond as the anode. The results showed that the electrochemical technique was able to completely mineralize the residual pollutants. The study of the influence of the supporting electrolyte on the electrochemical process showed that the trace mineral solution used in the biological treatment was enough to completely mineralize the oxyfluorfen, resulting in total organic carbon removal rates that were well-fitted by a first-order model with a kinetic constant of 0.91 h−1. However, the first-order degradation rate increased approximately 20% when Na2SO4 was added as supporting electrolyte, reaching a degradation rate of 1.16 h−1 with a power consumption that was approximately 70% lower.
•Low oxyfluorfen concentrations were completely removed by means of bioprocesses.•When operating with high oxyfluorfen concentrations product inhibition appeared.•Electrochemical treatment completely removed the non-biodegraded fraction.•Coupling biological and electrochemical processes ensure oxyfluorfen mineralization.•Na2SO4 as supporting electrolyte increased the first order rate in about 20%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Thermally sprayed Al and Al/SiC composite coatings have been deposited on pure magnesium and their corrosion behaviour in 3.5 wt.% NaCl solution has been studied. Al/SiC composite coatings were ...fabricated with 9 vol.% reinforcement percentage and with porosities around 3.5%, while the porosity of the as-sprayed pure Al coatings was in the range 2.4 vol.% to 4.4 vol.% and depended more on the spraying distance and numbers of layers deposited. A mechanical compaction was applied to the coatings at room temperature and coatings that were nearly free from pores were fabricated for the Al and Al/SiC coatings. In the electrochemical tests, all the coatings showed higher corrosion potentials (about of 200 mV) than uncoated substrates while current densities were nearly two orders of magnitude lower for the Al/SiC composite coatings and three orders of magnitude lower for the pure aluminium coatings. This protective effect was even better in the compacted coatings, currents densities were between five or six orders of magnitude lower than that of uncoated magnesium.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Intergranular corrosion behaviour of 316Ti and 321 austenitic stainless steels has been evaluated in relation to the influence exerted by modification of Ti, C and N concentrations. For this ...evaluation, electrochemical measurements – double loop electrochemical potentiokinetic reactivation (DL-EPR) – were performed to produce time–temperature–sensitization (TTS) diagrams for tested materials. Transmission (TEM) and scanning electron microscopy (SEM) were used to determine the composition and nature of precipitates. The addition of Ti promotes better intergranular corrosion resistance in stainless steels. The precipitation of titanium carbides reduces the formation of chromium-rich carbides, which occurs at lower concentrations. Also, the reduction of carbon content to below 0.03
wt.% improves sensitization resistance more than does Ti content. The presence of Mo in AISI 316Ti stainless steel reduces chromium-rich carbide precipitation; the reason is that Mo increases the stability of titanium carbides and tends to replace chromium in the formation of carbides and intermetallic compounds, thus reducing the risks of chromium-depletion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► Chemical conversion treatment in HF slows down biodegradation of Mg materials. ► In cell culture medium, MgF
2 coating retards corrosion process for at least a week. ► Coated cast Mg and AZ31 are ...promising candidates for biodegradable implants.
Mg-based materials are especially attractive as biodegradable implants, although they degrade so fast in physiological media that corrosion protection is needed. In this work, biodegradation kinetics of powder metallurgy Mg, cast Mg and AZ31 alloy were evaluated by EIS measurements in cell culture medium (DMEM), which simulates closely the physiological media. To reduce their degradation rate, a chemical conversion treatment in HF was applied to form MgF
2 coatings. Results confirmed that this coating slows down the biodegradation rate, especially when formed on cast Mg and AZ31, retarding the corrosion process in the cell culture medium for at least a week.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper addresses the influence of Cu and Sn addition on the corrosion resistance of AISI 304 and 316 stainless steels in 30 wt% H2SO4 at 25 and 50 deg C. The corrosion process was evaluated by ...gravimetric tests, DC measurements and electrochemical impedance spec-troscopy (EIS). The corrosion products were analysed by SEM, X-ray mapping and XPS before and after accelerated tests. The behaviour of both AISI 304 and 316 stainless steels in sulphuric acid solution was greatly improved by increasing Cu concentration and the synergic effect of Cu and Sn. Addition of Sn increased corrosion resistance, but less than addition of copper.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Pure magnesium was processed by a powder metallurgy (PM) route to generate microstructural features that provide higher mechanical properties than those of cast pure magnesium and commercial AZ31 ...alloy. Nevertheless, corrosion resistance of PM Mg needs to be improved if this material is to be used for structural applications in a corrosive medium. In the present work, the corrosion protection effectiveness of three simple, economical and environmentally friendly coatings has been evaluated over immersion time in a chloride-containing solution. A silane coating, an anticorrosive paint formulated with ion-exchangeable pigments (IEPs) and a chemical conversion treatment to form a MgF
2 layer have been studied. Silane film and anticorrosive paint enhance the corrosion behaviour of PM Mg during the first hours of immersion, but their protection effectiveness completely disappears after 2 days. For longer immersion times, the fluoride conversion coating may be considered the only viable and effective barrier to protect PM magnesium from degradation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Thermally sprayed Al and Al/SiCp composite coatings have been deposited on ZE41 magnesium alloy and mechanical compaction at room temperature was applied to the Al and Al/SiCp coatings to reduce ...their porosity. Corrosion behaviour of coated samples was evaluated and compared to that of uncoated substrate in 3.5
wt.% NaCl solution using electrochemical measurements. Al and Al/SiCp composite coatings reduced the corrosion current density of Mg–Zn alloys by three and two orders of magnitude, respectively, and reductions up to four orders of magnitude were obtained after mechanical compaction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The influence of silicon carbide (SiCp) proportion and matrix composition on four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) immersed in 1–3.5
wt% NaCl ...at 22
°C was investigated by potentiodynamic polarization. The kinetics of the corrosion process was studied on the basis of gravimetric measurements. The nature of corrosion products was analysed by scanning electron microscopy (SEM) and low angle X-ray diffraction (XRD). The corrosion damage in Al/SiCp composites was caused by pitting attack and by nucleation and growth of Al
2O
3
·
3H
2O on the material surface. The main attack nucleation sites were the interface region between the matrix and the reinforcement particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement and saline concentration.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The influence of Cu and Sn on the pitting corrosion resistance of AISI 304 and 316 stainless steels in chloride-containing media has been investigated. The corrosion behaviour was evaluated by cyclic ...polarization, potentiostatic CPT measurements and electrochemical impedance spectroscopy in 3.5
wt% NaCl. The corrosion resistance was also studied in FeCl
3 under Standard ASTM G-48. According to the results, Cu addition favours pit nucleation but inhibits its growth, whereas Sn exerts the opposite effect, favouring pit growth and inhibiting its nucleation. Studies by SEM, X-ray mapping and EDS analysis showed Cu-, Cl- and O-rich corrosion products that reduce the extent of corrosion damage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A new sensitive electrochemical technique is presented which is designed to measure the temperature dependence of the breakdown of passivity of metal surfaces. The method, termed “cyclic noise ...thermammetry”, consists of scanning the temperature of an electrochemical cell linearly and cyclically between two predefined limits, whilst simultaneously measuring the current flowing from a potentiostatically maintained microelectrode. An example of the new technique is presented, which describes the effect of temperature on the nucleation of corrosion pits on the titanium-based alloy, Ti–6Al–4V, in acidic chloride solution far below the pitting potential. Results are presented over the temperature range 20–50
°C. Events due to breakdown of passivity were detected throughout the entire temperature range. These events are the nucleation of corrosion pits, although they do not propagate into stable pits under the applied experimental conditions. Results show that passivity breaks down over the entire range of temperature, at a frequency that increases with increase in temperature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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