The corrosion of chromium based coatings for packaging steel

Chromium/chromium oxide based coatings, cathodically electrodeposited from either Cr (VI) or Cr (III) containing electrolytes are compared with respect to their ability to resist the corrosion driven delamination of an adherent polymer overcoat. Cathodic disbondment rates are determined using an in-situ scanning Kelvin probe technique. Anodic disbondment (filiform corrosion, FFC) rates are determined optically. The Cr (VI) derived coatings were fully resistant to corrosion driven disbondment. The Cr (III) derived coatings exhibited measurable rates of both FFC and cathodic disbondment. Disbondment kinetics are explained in relation to coating morphology, porosity and chemical composition determined using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and xray photoelectron spectroscopy (XPS)

Cyclic voltammetry study of trivalent basic chromium sulphate electrolytes contaminated with sulphite

Catalysis and Surface Chemistr

Electrocatalytic reduction of nitrate at low concentration on coinage and transition-metal electrodes in acid solutions

A comparative study was performed to determine the reactivity of nitrate ions at 0.1 M on eight different polycrystalline electrodes (platinum, palladium, rhodium, ruthenium, iridium, copper, silver and gold) in acidic solution using cyclic voltammetry (CV), chronoamperometry and differential electrochemical mass spectroscopy (DEMS). Cyclic voltammetry shows that the current densities for nitrate reduction depend strongly on the nature of the electrode. The activities decrease in the order Rh>Ru>Ir>Pd and Pt for the transition-metal electrodes and in the order Cu>Ag>Au for the coinage metals. The rate-determining step on Ru, Rh, Ir, Pt, Cu, and Ag is concluded to be the reduction of nitrate to nitrite, as is evident from the Tafel slope, the kinetic reaction order in nitrate, and the anion effect. Transfer experiments with Pt suggest that chemisorbed nitric oxide is the key surface intermediate in the nitrate reduction. Since on-line mass spectrometry (DEMS) measurements on Pt and Rh show no formation of gaseous products such as nitric oxide (NO), nitrous oxide (N2O) or nitrogen (N2), it is suggested that ammonia and hydroxylamine are the main products on transition-metal electrodes. This is in agreement with the known mechanism for NO reduction, which forms N2O or N2 only if NO is in solution. On Cu, DEMS measurements show the production of gaseous NO, which is explained by the weaker binding of NO to Cu as compared to the transition metals

Electrocatalytic reduction of nitrate at low concentration on coinage and transition-metal electrodes in acid solutions

A comparative study was performed to determine the reactivity of nitrate ions at 0.1 M on eight different polycrystalline electrodes (platinum, palladium, rhodium, ruthenium, iridium, copper, silver and gold) in acidic solution using cyclic voltammetry (CV), chronoamperometry and differential electrochemical mass spectroscopy (DEMS). Cyclic voltammetry shows that the current densities for nitrate reduction depend strongly on the nature of the electrode. The activities decrease in the order Rh>Ru>Ir>Pd and Pt for the transition-metal electrodes and in the order Cu>Ag>Au for the coinage metals. The rate-determining step on Ru, Rh, Ir, Pt, Cu, and Ag is concluded to be the reduction of nitrate to nitrite, as is evident from the Tafel slope, the kinetic reaction order in nitrate, and the anion effect. Transfer experiments with Pt suggest that chemisorbed nitric oxide is the key surface intermediate in the nitrate reduction. Since on-line mass spectrometry (DEMS) measurements on Pt and Rh show no formation of gaseous products such as nitric oxide (NO), nitrous oxide (N2O) or nitrogen (N2), it is suggested that ammonia and hydroxylamine are the main products on transition-metal electrodes. This is in agreement with the known mechanism for NO reduction, which forms N2O or N2 only if NO is in solution. On Cu, DEMS measurements show the production of gaseous NO, which is explained by the weaker binding of NO to Cu as compared to the transition metals

Oxidation reactions in chromium(III) formate electrolytes at platinum and at a catalytic mixed metal oxide coating of iridium oxide and tantalum oxide

Catalysis and Surface Chemistr

Electrocatalytic reduction of NO3- on palladium/copper electrodes

The reduction of NO3- on palladium/copper electrodes has been studied using differential electrochemical mass spectroscopy (DEMS), rotating ring-disk electrodes (RRDE) and quartz microbalance electrodes (ECQM). In acidic electrolytes, the activity increases linearly with Cu coverage, in alkaline electrolytes, a different dependence on coverage is observed. One monolayer of Cu gives a different selectivity from bulk copper. The adsorption of NO3- is competitive with SO42-, whereas Cl- adsorption blocks the reduction. Competitive adsorption lowers both the activity and the selectivity to N-2. Copper activates the first electron transfer, the role of palladium is to steer the selectivity towards N-2. The trends in activity and selectivity are explained in terms of coverage of N-species. (C) 2000 Elsevier Science B.V. All rights reserve

An Intelligent Ammonia Sensor for Livestock Breeding Monitoring

International audienceAmmonia concentration is the major parameter to evaluate livestock breeding farms atmosphere quality and it also is regarded as the key indicator to describe the production of livestock breeding farms. Based on the oxidation characteristics of ammonia, this paper presented a new intelligent detecting instrument, the intelligent ammonia sensor, for the measurement of ammonia concentration, which used the microcontroller STM8L152 as the key control module. However, the TEDS module, which is useful to self-identification, self-diagnosis and self-calibration of ammonia sensor, is in the flash of the STM8L152 and only if the STM8L152 conveys the warning signal to the alarm module, will the alarm module starts the worker loop

The role of adsorbates in the electrochemical oxidation of ammonia on noble and transition metal electrodes

The activity for ammonia oxidation and the intermediates formed during the reaction have been studied on platinum, palladium, rhodium, ruthenium, iridium, copper, silver and gold electrodes. The activity in the selective oxidation to N-2 is related directly to the nature of the species at the surface: the electrode is active if NHads (or NH2,ads) is present and deactivates when N-ads is present. The potential at which NHads or N-ads is formed is metal dependent. The observed trend in the strength of adsorption of N-ads is Ru > Ph > Pd > Ir > Pt much greater than Au, Ag, Cu. This trend corresponds well with the trend observed in the calculated heat of adsorption of atomic nitrogen, with iridium being an exception. Platinum is the best catalyst for this reaction because N-ads is formed at high potential, compared to rhodium and palladium, but seems to stabilize NHads rather well. Gold, silver and copper do not form NHads or N-ads, and show only an activity when the surface becomes oxidized. The metal electrodissolution is enhanced by ammonia under these conditions. Most metals produce oxygen- containing products, like NO and N2O, at potentials where the surface becomes oxidized. (C) 2001 Elsevier Science B.V. All rights reserve