Corrosion behaviour of Ni-Zr-Ti-Si-Sn amorphous plasma spray coating

Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ amorphous material was deposited by a vacuum plasma spraying technique onto steel and copper substrates in order to investigate their behaviour in a corrosive environment. For comparison, the same alloy was prepared as amorphous ribbons by melt spinning. The amorphous nature of the coatings and ribbons was characterized by XRD, DSC and TEM, while XPS and AES analyses were performed to understand the origin of passivation and mode of corrosion. The corrosion behaviour of the coating was studied in H₂SO₄ and HCl solutions open to air at room temperature. Potentiodynamic polarisation and galvanic coupling tests were carried out on the substrate and the coating. It was found that the formation of Zr-, Ti- and Si-rich passive oxide layers provide a high corrosion resistance in H₂SO₄ solution while the breakdown of the passive layer by chloride ion adsorption was responsible for pitting corrosion of the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ amorphous ribbons in HCl solution. Galvanic corrosion was the dominant corrosion mechanism for the coating/copper hybrid structure, in contrast to the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ amorphous coating, which efficiently protected the steel substrate in the corrosive environment.     

Influence of molybdenum on passivation of polarised stainless steels in a chloride environment

Polarised specimens of AISI 304L and 316L stainless steels (SS) were studied using X-ray photoelectron spectroscopy in conjunction with Ar⁺-ion sputtering. A 5% NaCl test solution was used at room temperature. The polarised passive films formed consist mainly of chromium oxide and hydroxide and a small proportion of iron oxides. The composition of the films depend strongly on the potential. Chloride and molybdenum ions appear when the AISI 316L SS alloy is polarised at a potential close to pitting potential.     

Preparation and characterisation of electrophoretically deposited hydroxyapatite coatings on type 316L stainless steel

Hydroxyapatite (HAP) coatings were developed on type 316L stainless steel (SS) by electrophoretic deposition at various deposition potentials from 30 to 90 V using the stoichiometric HAP (Ca/P ratio 1.67) powder in a suspension of isopropyl alcohol. The optimum coating parameters were established at 60 V and 3 min, after vacuum sintering at 800 °C. The phase purity of the coated surface was confirmed by XRD and secondary ion mass spectrometry confirmed the presence of both Ca and P on the coated layers. The electrochemical corrosion parameters E_corr (open circuit potential) and pitting potentials, evaluated in Hank’s solution shifted towards noble direction for the HAP coated specimens in comparison with uncoated type 316L SS. Electrochemical impedance spectroscopic investigations revealed higher polarisation resistance and lower capacitance values after immersing the coated specimens in Hanks solution for 200 h. This indicates the stable nature of the coatings formed.     

A comparative dielectric relaxation study of PMN–PT and PMN–PZ ceramics using impedance spectroscopy

AC-impedance spectroscopic studies in the temperature range of 30–400 °C are carried out on solid solutions of lead magnesium niobate (PMN) with lead titanate (PT) and lead zirconate (PZ), both of them in the 65/35 atomic ratio. For PMN–PT this corresponds to the morphotropic phase boundary composition (with normal ferroelectric behaviour), and for PMN–PZ it is near the phase boundary between normal ferroelectric and relaxor ferroelectric compositions. The variation of dielectric permittivity with temperature at different frequencies shows normal ferroelectric and relaxor-like dependence for PMN–PT and PMN–PZ, respectively. Temperature-dependent spectroscopic modulus plots reveal a much broader peak for PMN–PZ compared to that for PMN–PT, which is consistent with the dielectric behaviour. PMN–PT shows nearly ideal Debye behaviour below T_m (the temperature of the permittivity maximum) and the behaviour departs from ideality above T_m, whereas non-ideal Debye behaviour is seen both below and above T_m for PMN–PZ. Complex modulus plots fit well with two depressed semicircles and three depressed semicircles, respectively, for PMN–PT and PMN–PZ. The relaxation observed in the spectroscopic plots around 1 MHz for PMN–PT has been assigned to polarisation relaxation expected for normal-sized domains. No such relaxation could be observed for PMN–PZ around 1 MHz because of the mesoscopic domain sizes.     

The impact of porosity,pH2 and pH2O on the polarisation resistance of Ni–BaZr0.85Y0.15O3−δ cermet anodes for Protonic Ceramic Fuel Cells (PCFCs)

The effect of porosity and atmosphere on the polarisation resistance of Ni-BZY cermet anodes for protonic ceramic fuel cells (PCFCs) was investigated using electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The level of porosity was adjusted by the use of differing amounts of starch porogen. The total polarisation resistance of the cermet anode (Rp) generally showed an increase with increasing porosity. The high frequency polarisation resistance (R2) was shown to have low atmosphere dependence but presented a strong correlation to microstructural variations. In contrast, the low frequency polarisation resistance (R3) was shown to have a low dependence on humidity but demonstrated a strong negative dependence on pH₂ with a value of unity. Subsequent discussion relates the lower frequency response to the dissociative adsorption of H₂ on the anode surface. The present study highlights that porogens are not required for peak performance in PCFC anodes under standard operating conditions, a result contrary to that of their oxide-ion conducting cermet counterparts.     

The role of price as a product attribute in the organic food context: An exploration based on actual purchase data

High prices are often quoted as an obstacle to consumer purchase of organic food products. This article investigates the market performance of organic food products at different price levels and whether high price is necessarily a disadvantage for organic food products, especially with regard to generating repeat purchase. Based on analyses of panel purchase data from 2011 in Denmark, the study explores the effects of production method (organic vs. conventional) and price on consumers’ repeat purchase and cross-purchase across four product categories: red meat, chicken, milk and hard cheese. Results show that a high price is a disadvantage for generating repeat purchase of organic food products. Although organic products enjoy higher repeat purchase than conventional products overall, a high price generates less repeat purchase of organic products than a low or a medium price in all product categories; whereas in the case of conventional food products the situation is the reverse. At the same time, the cross-purchase analysis reveals that consumers who buy organic products from the high price tier are less likely to switch to other price tiers than consumers who buy low or medium price organic products (i.e. there is a spillover of high price organic food purchases to other product categories). Implications for pricing strategies for organic food products are discussed.     

Electrochemical and corrosion behaviour of stainless steels 316L and 317L in chloridised ammonium sulphate solution

Abstract

The corrosion of stainless steel alloys 316L and 317L in chloridised ammonium sulphate solution at 100°C and varying pH was investigated. Alloy 316L was found to be an adequate material for use in naturally aerated solution within the pH range of 5·4–7·4. At low potentials (<0·23 V) and a high potential (0·75 V), alloy 317L shows better performance. It also exhibits better pitting resistance at high potential, however, in the potential range of 0·23–0·45 V, alloy 316L shows better corrosion resistance. The dissolution of the Mo oxide species is proposed to be the reason for the weak performance of alloy 317L in the potential range of 0·23–0·45 V.

On a examiné la corrosion des aciers inoxydables 316L et 317L dans une solution chlorée de sulfate d’ammonium à 100°C et à pH variable. On a trouvé que l’alliage 316L était un matériel adéquat pour utilisation dans une solution aérée naturellement dans la gamme de pH de 5·4 à 7·4. Aux faibles potentiels (<0·23 V) et à potentiel élevé (0·75 V), l’alliage 317L montrait une meilleure performance. Il exhibait également une meilleure résistance à la corrosion par piqûres à potentiel élevé. Cependant, dans la gamme de potentiel de 0·23–0·45 V, l’alliage 316L montrait une meilleure résistance à la corrosion. On propose la dissolution d’une espèce d’oxyde de Mo comme étant la raison pour la faible performance de l’alliage 317L dans la gamme de potentiel de 0·23–0·45 V.     

Influence of electron beam liquid phase surface treatments on the corrosion resistance of AZ91D using different additive deposition techniques

Electron beam alloying (EBA) and electron beam cladding (EBC) were applied on AZ91D using Al-based additives. For EBA, additives were pre-deposited by atmospheric plasma spraying (APS) and cold gas spraying (CGS). In the case of EBC, a wire was used for in situ additive deposition. Polarisation test were carried out to investigate the corrosion behaviour of layers with Mg-rich (EBA) and Al-rich (EBC) layer matrices depending on the element contents of Mg, Al, and Si. In 0.001 M NaCl solution, the corrosion potential is significantly improved compared with the untreated AZ91D and corrosion current densities of the AlSi12 reference material are approached.     

The influence of electrolyte reduction potential on weld corrosion

Electrochemical potentiodynamic sweeps and galvanic studies are performed to determine conditions that will initiate localized corrosion in welded areas. The reduction potential and pH in the electrolyte seemed to be essential with respect to where corrosion attacks occur in a welded area of carbon steel. The interpretation of the polarization diagrams for the different parts of the weld showed that they actually had different anodic Tafel slopes and this interpretation could be used to make predictions concerning preferential corrosion behavior. A variance of brine composition causes a change of attacked areas in a weld.     

Critical pitting temperature dependence of 2205 duplex stainless steel on dichromate ion concentration in chloride medium

In this study, the influence of various concentrations of dichromate and chloride ions on critical pitting temperature (CPT) of duplex stainless steel 2205 (DSS 2205) is investigated by employing potentiodynamic and potentiostatic CPT measurement methods. Potentiostatic results indicate that by adding 0.01 M to 0.1 M NaCl solution the CPT raised by 12 °C. Based on potentiodynamic CPT measurements in the solutions with ratio equal to one for solutions containing 0.1 M NaCl + 0.1 M and 0.01 M NaCl + 0.01 M , no CPT was detected up to 75 °C.