1,721,159 research outputs found
Corrosion behaviour assessment of cast and HIPed Stellite 6 alloy in a chloride-containing environment
No full textCobalt-base (Stellite) alloys have seen extensive use in wear environments mainly due to their high strength, corrosion resistance and hardness. Co-base superalloys rely primarily on carbides formed in the Co matrix and at grain boundaries, for their strength and wear resistance. The distribution, size and shape of carbides depend on processing conditions. Currently, the use of Stellite alloys has extended into various industrial sectors (e.g. pulp and paper processing, oil and gas processing, pharmaceuticals, chemical processing) and the need for improved information regarding corrosion of Stellite alloys has increased. It has been recognized that processing changes, which affect the microstructure of Stellite alloys, most affect corrosion resistance. In this work the corrosion behaviour of Stellite 6 alloy in the as-cast and the HIPed consolidated forms is compared and contrasted using DC and AC electrochemical techniques in static saline conditions. The results show that there is a significant difference in the corrosion performance of HIP consolidated Stellite 6 and it is possible to link the corrosion behaviour to the microstructure. The benefits of using HIPing as a manufacturing process for the corrosion performance of Stellite 6 are discussed
Electrocatalytic activity of Ni-Fe-M (M = Cr, Mn, Cu) sintered electrodes for hydrogen evolution reaction in alkaline solution
No full textTernary Ni60Fe30M10 (M = Cr, Mn, Cu) sintered alloys have been characterized by means of microstruc- tural and electrochemical techniques in view of their possible applications as electrocatalytic materials for hydrogen evolution reaction (HER). Well-mixed powders of nickel, iron and copper, manganese, or chromium were pressed together under high pressure at room temperature and then sintered in vac- uum at high temperature. The surface morphology of the alloys was examined by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS). The electrochemical effi- ciency of the electrodes has been studied on the basis of electrochemical data obtained from steady- state polarization and electrochemical impedance spectroscopy (EIS) techniques in 1 M NaOH solution at 298 K. The results were compared with those obtained on binary Ni60Fe40 sintered alloy. The overall experimental data indicate that alloying Ni-Fe with Cr, Mn and Cu leads to an increase of electrocat- alytic activity in hydrogen evolution with respect to the Ni60Fe40 electrode. High catalytic efficiencies were achieved on Ni60Fe30Mn10 and Ni60Fe30Cr10 electrodes, the latter being the best electrocatalyst for the HER
Influenza del trattamento di kolsterizzazione sulla resistenza a corrosione dell’acciaio inossidabile AISI 204Cu
Full text linkI trattamenti termochimici per incrementare la durezza superficiale degli acciai come
cementazione e nitrurazione sono stati largamente studiati in passato; questi
trattamenti portano ad ottenere una durezza superficiale che raggiunge anche i 1200
HV. Tuttavia, considerando gli acciai inossidabili austenitici (alti tenori di Cr e Ni), i
trattamenti termochimici, se effettuati a temperature superiori ai 500°C, provocano la
precipitazione di carburi o nitruri di cromo i quali, impoverendo la matrice
nell’elemento che conferisce l’inossidabilità, riducono le proprietà anti-corrosive dei
suddetti acciai. Negli ultimi tempi si sta diffondendo un nuovo tipo di trattamento
termochimico chiamato Kolsterizzazione, che può definirsi una cementazione in
bassa temperatura (< 470°C). Questo trattamento permette anch'esso l’arricchimento
superficiale di C, tuttavia, essendo effettuato a temperature minori della classica
cementazione, evita la precipitazione dei carburi di Cr che comprometterebbero la
resistenza alla corrosione degli acciai austenitici.
Il presente lavoro ha inteso studiare le possibili modifiche superficiali indotte dal
trattamento di Kolsterizzazione e il loro effetto sulla resistenza a corrosione di un
particolare tipo di acciaio inossidabile austenitico al Cr-Mn, l’ AISI 204Cu, introdotto
nel 2001 come possibile sostituto dell’acciaio AISI 304. Il trattamento termochimico
provoca la precipitazione di due differenti tipologie di carburi: Fe2,5C (carburo di Hagg)
e Fe2C. La loro presenza, tuttavia, non sembra incidere così negativamente sul
comportamento a corrosione dell’acciaio kolsterizzato che risulta superiore a quella
del materiale base.
ABSTRAC
Corrosion inhibition of high strength maraging steel by cerium(III) ions in sulfuric acid solution
No full textThe influence of rare earth Ce(III) ions on the corrosion behaviour of high strength maraging steel in 0.5 M sulfuric acid solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Ce3þ can significantly reduce corrosion deterioration up to 5.0 mM. Beyond that level the corrosion rate increases till a steady value. High corrosion protection of steel surface after exposure to the acidic solution containing the optimal Ce(III) concentration is revealed by SEM investigation
Influence of cerium(III) ions on corrosion of TRIP 800 steel in hydrochloric acid solution
No full textCe(III) was studied for its corrosion inhibition property on the corrosion of TRIP 800 C-Mn-Si steel in 0.5 M hydrochloric acid at 258C by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. SEM was used to examine the specimen surface exposed to 0.5 M HCl containing the optimal threshold Ce(III) concentration (2.5 mM). A model for the corrosion process mechanism and inhibition by Ce(III) salt for TRIP 800 steel in the tested medium is proposed
Hydrogen Evolution Reaction on Magnetron Sputtering Deposited Nanocrystalline Nickel Film
No full textThe Mirrors of Villa della Regina in Turin: Study of Manufacturing and Deterioration Process
No full textA study has been carried out in order to investigate the manufacturing and the deterioration processes of tin-mercury mirrors, coming from the Villa della Regina, in Turin, a prestigious Savoy residence built in the seventeenth century and currently under restoration. The mirrors are backed with a tin-mercury amalgam as a reflective coating which is a two-phase system (a tin-mercury compound surrounded by a liquid phase rich in mercury); this layer is not stable, because the crystals grow and the mercury slowly evaporates, moreover the corrosion phenomena lead to the formation of SnO and SnO2 and to the release of liquid mercury from the solid phase. Microchemical and microstructural analyses have been performed by means of scanning electron microscopy equipped with X-ray spectrometry (SEM+EDS) and by means of X-ray diffraction (XRD) on fragments of the tin-mercury mirrors removed from the looking-glasses for restoration purposes and on experimental mirrors produced for comparison purposes following the ancient manufacturing receipt. The experimental mirrors have been made by laying down a thin sheet of tin on a flat marble surface, by pouring successively mercury on the tin and finally by pressing a glass sheet on the top. The reaction starts immediately and lasts within one or two days. The experimental mirrors have been submitted to ageing tests in a climatic chamber, in order to simulate the deterioration process. The corrosion of tin-mercury mirrors is an extremely slow process, as a matter of fact, on all the old mirrors fragments analyzed a certain amount of liquid mercury is still present. The old mirrors show several dark areas, where the brightness is disappeared. In the corroded areas cassiterite and romarchite, two typical atmospheric-corrosion products of the tin-rich phases, have been identified by XRD analysis. There is no way to prevent the deterioration process of the tin-mercury mirrors; it must be avoided the contact with materials that may react with mercury; furthermore, the amalgam reflecting layer is very soft, thus any restoration is difficult to perform and may lead to a complete destruction of the artefact. A restoration method is proposed here based on an amalgam inlay produced in-situ on the corroded zone of the mirror
Investigation of passivity and its breakdown on Fe3Al–Si and Fe3Al–Ge intermetallics in chloride-containing solution
No full textThe passivity and passivity breakdown of Fe3Al–Si and Fe3Al–Ge iron aluminides were studied in borate
buffer solution (pH 8.4) in the absence and presence of 100 mM KCl, performing potentiodynamic polar-
ization, potentiostatic transients and electrochemical impedance spectroscopy (EIS) measurements com-
plemented with scanning electron microscopy (SEM). In the absence of chloride ions Si and Ge exercise a
beneficial role in the passivating characteristics of Fe3Al intermetallic. Addition of Si or Ge significantly
modifies the electrochemical response of iron aluminide Fe3Al resulting in a more stable passive film.
In the presence of chloride ions all the intermetallic compounds experience localized corrosion (pitting).
However, Si and Ge alloying additions increase the breakdown potential and the extent of passivation
domain, indicating improved resistance to initiation of pitting corrosion. Furthermore, EIS measurements
performed at the breakdown state evidenced higher Rct and lower depression angle values for Fe3Al–Si
and Fe3Al–Ge iron aluminides compared to Fe3Al intermetallic, confirming their better localized corro-
sion behavior. The improved resistance to pitting corrosion results from the enhanced protective function
of passive film due to the presence of Si or Ge that inhibit pit initiation by hindering the adsorption of ClÀ
ions at the metal surface
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