Incipient Precipitation Research Articles

Suspended and deposited microplastics in the coastal atmosphere of southwest England

Atmospheric microplastics (MPs) have been sampled from coastal southwest England during twelve periods over a 42-day timeframe in late autumn. MPs were dominated by fibres, with foams, fragments and pellets also observed. The majority of fibres were identified as the semisynthetic polymer, rayon, while other shapes were dominated by various petroleum-based thermoplastics (including polyvinyl acetate, polyvinyl alcohol, polyamide and polyester) and paints. MP concentrations suspended in air ranged from 0.016 to 0.238 items per m3 but displayed no clear dependence on wind speed or direction. Total depositional fluxes ranged from 0.47 to 3.30 m−2 h−1 and showed no clear dependence on wind conditions or electrical conductivity of precipitation (as a measure of maritime influence). However, the concentration of deposited MPs in rainwater was inversely related to rainfall volume, suggesting that incipient precipitation acts to efficiently washout microplastics. A comparison of deposited and suspended MPs by size, shape and polymer type suggests that larger fibres constructed of rayon, polyamide and acrylic are preferentially removed from the atmosphere relative to smaller, non-fibrous MPs and particles constructed of polyester. A quantitative comparison of deposited and suspended MPs provided estimates of location- and environment-specific net settling velocities of between about 7 and 180 m h−1 and corresponding residence times for an air column of 5000 m of between about 30 and 700 h. The findings of the study contribute to an improved understanding of the occurrence, transport and deposition of MPs in the atmosphere more generally.

Thermodynamic Study on the Dissociation and Complexation of Coumarinic Acid with Neodymium(III) and Dioxouranium(VI) in Aqueous Media

In the frame of a systematic study on the sequestering ability of natural antioxidants towards metal cations, the complexation of coumarin-3-carboxilic acid (HCCA) with neodymium(III) and dioxouranium(VI) (uranyl, UO22+), and overall stability constants of the resulting complexes, were evaluated from the pH-potentiometric titration data at 37 °C and in an aqueous solution (i.e., 0.16 mol/L NaClO4). The graphic representation of the complex’s concentration curves is given by the distribution diagrams, which provide a depiction of all the species present in the solution in the selected pH ranges. The protonation constant of HCCA was also determined to evaluate the competition of the ligand for the metal cations and H+. The ligand-to-metal concentration ratio was varied between 1 and 10, and the hydrogen ion concentration was decreased stepwise until the incipient precipitation of a basic salt of the metal, which occurred at different values depending on the specific metal cation and the ligand to metal ratio. Speciation profiles obtained by potentiometric titrations and supported by UV-Vis data show that a complexation occurs at a ligand-to-Nd(III) and to –UO22+ ratio of 1:1 and 2:1, with different degrees of deprotonation: Nd(OH)(CCA)+, UO2(OH)(CCA), UO2(OH)2(CCA)−, and Nd(OH)(CCA)2, UO2(CCA)2 and (UO2)2(OH)2(CCA)2.

Study of Complexation Equilibria Between the Iron(III) Ion and 2-Hydroxybenzamide in Aqueous Solution

The complexation of the Fe3+ ion with 2-hydroxybenzamide (salicylamide, HL) has been studied, at 25.0 °C, by potentiometric measurements with a glass electrode in 1 mol·dm−3 NaClO4 medium. The concentration of salicylamide (C L) has been varied between (1 × 10−3 and 10 × 10−3) mol·dm−3, while the concentration of metal cation (C M) ranged within (0.5 × 10−3 and 10 × 10−3) mol·dm−3. The ligand to metal concentration ratio has been varied between 1 and 10 and the hydrogen ion concentration was decreased stepwise until the incipient precipitation of a basic salt of the metal, which occurred at different values depending on the specific ligand to metal ratio. The experimental data were consistent with the formation of the complexes FeL2+, Fe(HL)L2+ and $$ {\text{FeL}}_{2}^{ + } $$ . Equilibrium formation constants have been given for the investigated ionic medium as well as for the infinite dilution reference state, evaluated according to the Specific Interaction Theory. The predominant species in neutral solution are $$ {\text{FeL}}_{2}^{ + } $$ and $$ {\text{Fe}}\left( {\text{OH}} \right)_{2}^{ + } $$ .

Rheological and optical investigation of the gelation with and without phase separation in PAN/DMSO/H2O ternary blends

Thermal-induced gelation and phase separation was investigated in PAN/DMSO/H2O semidilute solutions utilizing rheological and optical methods. The incipient precipitation temperature, where a distinct decrease in relative light transmittance occurred, was considered as the cloud point (CP). Phase separation mechanism of nucleation and growth was confirmed by various ramp rates experiments and viscoelastic evolution pattern. On the other hand, the validity of Chambon–Winter model was evaluated in these blends and used to measure the critical gel point (GP). It was found that in the accessible temperature regions CP was always higher than GP, and phase boundaries were constructed accordingly. What's more, the absolute complex viscosity η′ at a low frequency also showed transition points during temperature decreasing experiments, which mostly located between CPs and GPs. The gelation mechanisms with and without phase separation were proposed and the effect of the two transitions on the structures of the ternary blends were shown by SEM pictures.

Evaporation of a sodium chloride solution from a saturated porous medium with efflorescence formation

AbstractPrecipitation of sodium chloride driven by evaporation at the surface of a porous medium is studied from a combination of experiments, continuum simulations, pore network simulations and a simple efflorescence growth model on a lattice. The distribution of ions concentration maxima at the porous medium surface, which are seen as the incipient precipitation spots, is shown to be strongly dependent on the factors affecting the velocity field within the porous medium owing to the significance of advection on ion transport. These factors include the evaporation flux distribution at the surface at Darcy’s scale as well as the scale of surface menisci and the internal disorder of the porous medium, which induce spatial fluctuations in the velocity field. The randomness of the velocity field within the porous medium and at its surface explains the discrete nature of incipient precipitation spots at the surface of a porous medium. Experiments varying the mean size of the beads forming the porous medium lead to the identification of two main types of efflorescence, referred to as crusty and patchy, and the impact of these two types on evaporation is completely different. The crusty efflorescence severely reduces the evaporation rate whereas the patchy efflorescence can enhance the evaporation rate compared with pure water. The crusty–patchy transition is analysed from a simple growth model on a lattice taking into account the porous nature of efflorescence structures.

Development of permanganate assisted manganese phosphate coating on mild steel

Manganese phosphate coatings are widely used as pretreatment for corrosion and wear resistance of numerous automotive components. Manganese phosphating formulations are established with various additives to improve the coating weight besides achieving the required amount of iron dissolution in a shorter time. The aim of our investigation is to use permanganate as an additive to increase iron dissolution and to achieve subsequent improvement in the quality of manganese phosphate coating. Manganese carbonate, phosphoric acid, nitric acid are used to create a basic formulation in which permanganate concentration is varied. The composition of the final formulation is optimised by giving due consideration to higher iron dissolution and improved coating weight. The resultant coating is characterised with polarisation, electrochemical impedance spectroscopy (EIS), FT-IR, XRD, SEM and EDX. The kinetics of the coating formation is also followed using potential–time measurement for all the experimental baths. Kinetic studies showed earlier attainment of point of incipient precipitation of manganese phosphate coating in the optimised formulation when compared to other formulation under investigation. The study revealed that the addition of KMnO4 in the manganese phosphating bath enabled an increase in the rate of metal dissolution, and enrichment of ferrous ion concentration at the metal/solution interface thus, favoured precipitation of corrosion and wear resistant Hureaulite ((Mn,Fe)5H2(PO4)4.4H2O). For a given coating weight, addition of KMnO4 substantially reduced the processing time.

Microtexture and Distribution of Minerals in Hydrothermal Barite‐Silica Chimney from the Franklin Seamount, SW Pacific: Constraints on Mode of Formation

AbstractAn extinct hydrothermal barite‐silica chimney from the Franklin Seamount of the Woodlark Basin, in the southwestern Pacific Ocean, was investigated for mineral distribution and geochemical composition. Six layers on either side of the orifice of a chimney show significant disparity in color, mineral assemblage and major element composition. Electron microscope (SEM) images reveal that the peripheral wall of the chimney is composed of colloform silica, suggesting that incipient precipitation of silica‐saturated hydrothermal fluid initiated the development of the chimney wall. Intermediate layers, between the exterior wall and the inner fluid‐orifice, dominate with barite and sulfides. Low Sr‐to‐Ba ratios (SrO/BaO = 0.015–0.017) indicate restricted fluid‐seawater mixing, which causes relatively high‐temperature formation of the intermediate layers. Whereas the innermost layer bordering the chimney orifice is characterized by more silica and a higher Sr‐to‐Ba ratio (SrO/BaO = 0.023), could have formed due to a paragenetic shift from a high‐temperature active phase to a cooler waning stage of formation. A paragenetic shift is also probably responsible for the change in mineral formation mechanism that resulted in the textural variation of barite and colloform silica developed during different growth phases of this barite‐silica chimney.

Kinetics of Precipitation Behavior of Second Phase Particles in Ferritic Ti-Mo Microalloyed Steel

Two types of stress relaxation tests were carried out to investigate the incubation time for incipient precipitation of Ti(C,N) in deformed austenite and (Ti, Mo)C in ferrite of ferritic Ti-Mo microalloyed steel. The size distribution, amount and chemical composition of precipitates were obtained by using physicochemical phase analysis, and calculated according to thermodynamics and kinetics. The experimental results demonstrated that the incubation time was reduced with increasing Ti content, and prolonged with the addition of Mo. After 30% deformation at 850 °C, the nucleation of strain-induced Ti(C,N) was a relatively slow process. On the other hand, the temperature where the nucleation rate of (Ti, Mo)C in ferrite was the highest descended first and then ascended with increasing Ti content, and so did the temperature where the incubation time was the shortest. The key point is that the temperature of steel containing about 0. 09% Ti is the lowest. The mass fraction of MC-type particles with size smaller than 10 nm in steel containing 0. 09% Ti and 0. 2% Mo reached 73. 7%. The size distributions of precipitates in steel containing 0. 09% Ti were relatively concentrated compared with that in steel containing 0. 07% Ti.

Speciation of 2-Hydroxybenzoic Acid with Calcium(II), Magnesium(II), and Nickel(II) Cations in Self-Medium

Equilibria occurring between 2-hydroxybenzoic acid (salicylic acid, H2L) and calcium(II), magnesium(II), and nickel(II) have been studied by potentiometric titrations with glass electrodes at 298.15 K in self-medium constituted of 1.05 mol·kg–1 NaHL. The self-medium composition can be considered constant since only a small amount of ligand HL– is transformed in the reaction products. The hydrogen ion concentration was varied from 10–2 mol·kg–1 to incipient precipitation of a basic salt of each metal, whose formation depends on the particular metal. The total metal concentration, CM, ranged from 3.05·10–3 mol·kg–1 to 10.01·10–3 mol·kg–1. The higher CM value was imposed in order to avoid changes in the ionic medium and in the activity coefficients. The experimental data have been explained by assuming the formation of the complexes: CaL; MgL, MgL22–, and MgL34–; NiL and NiL22–.

Interaction of Iron(III) with 2-Hydroxybenzoic Acid in Aqueous Solutions

The complex formation between the Fe3+ ion and 2-hydroxybenzoic acid (salicylic acid, H2L) has been studied at 298.15 K in 1.05 mol·kg–1 NaClO4 medium by both potentiometric titrations with glass electrodes and spectrophotometric measurements in the range of wavelengths between (410 and 600) nm. The concentrations of ligand (CL) and metal ion (CM) were varied between (0.105 × 10–3 and 21 × 10–3) mol·kg–1, and the ligand-to-metal ratio was varied between (1 and 1000) (1 ≤ CL/CM ≤ 1000). The hydrogen ion concentration was decreased stepwise to the incipient precipitation of a basic salt of metal. The experimental data have been explained with the formation of the complexes FeL+, FeL2–, FeL33–, Fe(HL)L, and Fe2(OH)2(HL)L+. Stability constants for their formation in 1.05 mol·kg–1 NaClO4 as well as in dilute solution are reported.

Polarization and impedance studies on zinc phosphate coating developed using galvanic coupling

Galvanic coupling technique is capable of producing coatings of desired thickness. Good quality coatings can be produced at low temperature. Galvanic coupling of mild steel (MS) with the other cathode materials such as titanium (Ti), copper (Cu), brass (BR), nickel (Ni), and stainless steel (SS) accelerates iron dissolution, enables quicker consumption of free phosphoric acid and facilitates an earlier attainment of point of incipient precipitation, resulting in a higher amount of coating formation. In the present investigation, potentiodynamic polarization and electrochemical impedance spectra on MS substrates phosphated using galvanic coupling are studied. This study reveals that MS substrates phosphated under galvanically coupled condition possess better corrosion resistance than the substrates phosphated under uncoupled condition.

Microstructural characterization by electron backscatter diffraction of a hot worked Al–Cu–Mg alloy

Hot torsion tests to fracture to simulate thermomechanical processing were carried out on a solution-treated Al–Cu–Mg alloy (Al 2024-T351) at constant temperature. Torsion tests were conducted in the range 278–467 °C, and at two strain rates, 2.1 and 4.5 s −1. Electron backscatter diffraction (EBSD) was employed to characterize the microtexture and microstructure before and after testing. The microstructural evolution during torsion deformation at different temperatures and strain rate conditions determines the mechanical properties at room temperature of the Al 2024 alloy since grain refining, dynamic precipitation and precipitate coalescence occur during the torsion test. These mechanical properties were measured by Vickers microhardness tests. At 408 °C and 2.1 s −1 the optimum combination of solid solution and incipient precipitation gives rise to maximum ductility and large fraction of fine and misoriented grains ( f HAB = 54%). In contrast, the increase in test temperature to 467 °C produces a sharp decrease in ductility, attributed to the high proportion of alloying elements in solid solution. Both the stress–strain flow curves obtained by torsion tests and the final microstructures are a consequence of recovery phenomena and the dynamic nature of the precipitation process taking place during deformation.

Complexation of l-Cystine with Metal Cations

The complexation equilibria of l-cystine, H2L, with the Cu2+, Al3+, and Fe3+ ions have been studied at 25 °C and in 3 mol·dm−3 NaClO4 ionic medium by potentiometric measurements with a glass electrode. The concentrations of ligand (CL) and metal ions Mz+ (CM) were varied between (0.5·10−3 and 5·10−3) mol·dm−3, and the ligand-to-metal ratio was varied between 1 and 10 (1 ≤ CL/CM ≤ 10). The hydrogen ion concentration was decreased stepwise to the incipient precipitation of a basic salt of each metal. The experimental data have been explained with the formation of the complexes: CuL, CuL22−, Cu(HL)2, and Cu2(HL)3+; AlL+ and AlL2−; and FeL+ and FeL2−. Equilibrium formation constants are given for the investigated ionic medium as well as for the infinite dilution reference state, evaluated by the specific ion interaction theory (SIT).

Preparation of Pt/C electrocatalysts using an incipient precipitation method

Highly loaded and dispersed Pt/C catalysts, used as cathodic electrocatalysts in low temperature fuel cells, were prepared using a new method involving the slow addition of a Pt precursor to a solution containing dispersed carbon powder and a reducing agent. During this process, the added Pt precursor was reduced instantaneously into fine particles and adsorbed onto the carbon surface in the solution. A Pt loading of 55 wt% was obtained, which was close to the nominal amount of Pt, 60 wt%, added in the preparation step. The average particle size of Pt was about 4.2 nm, according to X-ray diffraction. The surface area of the Pt measured by cyclic voltammetry was about 61.4 m 2 /(g of Pt). The activity of the prepared Pt/C, as an electrode of polymer electrolyte membrane fuel cell, was increased by 34.8% and 15.0%, according to the half- and single-cell tests, respectively, compared to the activity of one prepared using a conventional precipitation method.

2-Hydroxybenzamide as a Ligand. Complex Formation with Dioxouranium(VI), Aluminum(III), Neodymium(III), and Nickel(II) Ions

The complexation equilibria of 2-hydroxybenzamide (salicylamide, HL) with UO 2 2+ , Al 3+ , Nd 3+ , and Ni 2+ ions have been studied at 25 °C and in 1 mol·dm -3 NaClO 4 ionic medium by potentiometric measurements with a glass electrode. The concentration of ligand (C L ) was varied between (1·10 -3 and 15·10 -3 ) mol·dm -3 , while the concentration of metal ions M z+ (C M ) ranged within (0.5·10 -3 and 10·10 -3 ) mol·dm -3 . The ligand to metal concentration ratio was varied between 1 and 20. The hydrogen ion concentration was decreased stepwise to the incipient precipitation of a basic salt of each metal. The experimental data have been explained with the formation of the complexes: UO 2 L + , UO 2 L 2 , UO 2 (HL)L + , UO 2 (OH)L, (UO 2 ) 2 (OH)L 2 + , (UO 2 ) 2 (OH) 2+ 2 , and (UO 2 ) 3 (OH) + 5 ; AlL 2+ , AlL 2 + , Al(OH)L 2 , AlOH 2+ , Al(OH) + 2 , and Al 3 (OH) 5+ 4 ; NdL 2+ , NdL + 2 , NdOH 2+ , and Nd 2 OH 4+ 2 ; and NiL + , Ni(OH)L, and NiOH + . Equilibrium formation constants are given for the investigated ionic media as well as for the infinite dilution reference state, evaluated by the specific ion interaction theory (SIT).

Segregative interactions and competitive binding of Ca 2+ in gelling mixtures of whey protein isolate with Na +κ-carrageenan

Gelling mixtures of Na + κ-carrageenan with whey protein isolate (WPI) at pH 7.0 have been studied rheologically and by differential scanning calorimetry (DSC), with comparative measurements for the individual constituents of the mixtures. The concentration of WPI was held fixed at 10.0 wt% and carrageenan concentration was varied in the range 0.05–3.0 wt%. Ca 2+ cations, which have been shown previously to be particularly effective in inducing gelation of κ-carrageenan, were introduced as CaCl 2. The concentration of CaCl 2 used in most of the experiments was 8 mM, but other concentrations were also studied. Mixtures were prepared in the solution state at 45 °C, and showed no evidence of either phase separation or complex formation. Rheological changes were monitored by low-amplitude oscillatory measurements of storage modulus, G′, during (i) cooling (1 °C/min) and holding at 5 °C, to induce gelation of the carrageenan in the presence of non-gelled WPI; (ii) heating and holding at 80 °C to dissociate the carrageenan network and induce gelation of WPI; (iii) cooling and holding again at 5 °C, to give composite networks with both components gelled; and (iv) re-heating to 80 °C to dissociate the carrageenan network. Gel structure was characterised further by creep–recovery measurements at the end of each holding period, and by torsion measurements at 5 °C, before and after thermal gelation of WPI. In 8 mM CaCl 2, the presence of 10.0 wt% WPI promoted earlier gelation of κ-carrageenan during cooling, and displaced the disorder–order transition in DSC to higher temperature. These changes are attributed to segregative interaction with non-gelled WPI. The resulting networks, however, were weaker that those formed by κ-carrageenan alone, which was traced to binding of Ca 2+ cations to the WPI. At higher concentrations of CaCl 2, where availability of Ca 2+ cations was no longer a limiting factor in gelation of the κ-carrageenan, the effect of segregative interactions could be seen as an increase in gel strength. On heating to gel the WPI, the presence of κ-carrageenan led to the earlier appearance of an aggregation exotherm in DSC and to network formation at shorter times, which can similarly be explained by enhanced self-association of denatured WPI in response to segregative interactions with disordered carrageenan. An initial large (∼10 fold) increase in gel strength with increasing concentration of carrageenan to ∼0.25 wt% was followed by a reduction at higher concentrations, attributed to excessive aggregation (incipient precipitation) of the WPI. The magnitude of the changes in G′ observed on subsequent cooling suggest that gelation of κ-carrageenan within the pores of an existing network of gelled WPI gives rise to a bicontinuous co-gel structure. Comparison of moduli at 80 °C before and after cooling to 5 °C demonstrated that formation and dissociation of the carrageenan network caused no disruption of the network of gelled WPI.

Reversible expansion of gallium-stabilized δ-plutonium

It is shown that the transient expansion of plutonium–gallium alloys observed both in the lattice parameter as well as in the dimension of a sample held at ambient temperature can be explained by assuming incipient precipitation of Pu 3Ga. However, this ordered ζ′-phase is also subject to radiation-induced disordering. As a result, the gallium-stabilized δ-phase, being metastable at ambient temperature, is driven towards thermodynamic equilibrium by radiation-enhanced diffusion of gallium and at the same time reverted back to its metastable state by radiation-induced disordering. A steady state is reached in which only a modest fraction of the gallium present is arranged in ordered ζ′-phase regions.

Observational Diagnosis and Model Forecast Evaluation of Unforecasted Incipient Precipitation during the 24–25 January 2000 East Coast Cyclone

Abstract Previous research has shown that a lower-tropospheric diabatically generated potential vorticity (PV) maximum associated with an area of incipient precipitation (IP) was critical to the moisture transport north of the PV maximum into the Carolinas and Virginia during the 24–25 January 2000 East Coast cyclone. This feature was almost entirely absent in short-term (e.g., 6–12 h) forecasts from the 0000 UTC 24 January 2000 operational runs of the National Centers for Environmental Prediction (NCEP) North American Mesoscale (NAM, formerly Eta) and Global Forecast System (GFS, formerly AVN) models, even though it occurred over land within and downstream of a region of relatively high data density. Observations and model analyses are used to document the forcing for ascent, moisture, and instability (elevated gravitational and/or symmetric) associated with the IP, and the evolution of the IP formation is documented with radar and satellite imagery with the goal of understanding the fundamental nature of this precipitation feature and the models’ inability to predict it. Results show that the IP formed along a zone of lower-tropospheric frontogenesis in a region of strong synoptic-scale forcing for ascent downstream of an approaching upper trough and jet streak. The atmosphere above the frontal inversion was characterized by a mixture of gravitational conditional instability and conditional symmetric instability over a deep layer, and this instability was likely released when air parcels reached saturation as they ascended the frontal surface. The presence of elevated convection is suggested by numerous surface reports of thunder and the cellular nature of radar echoes in the region. Short-term forecasts from the Eta and AVN models failed to capture the magnitude of the frontogenesis, upper forcing, or elevated instability in the region of IP formation. These findings suggest that errors in the initial condition analyses, particularly in the water vapor field, in conjunction with the inability of model physics schemes to generate the precipitation feature, likely played a role in the operational forecast errors related to inland quantitative precipitation forecasts (QPFs) later in the event. A subsequent study will serve to clarify the role of initial conditions and model physics in the representation of the IP by NWP models.

The Influence of Incipient Latent Heat Release on the Precipitation Distribution of the 24–25 January 2000 U.S. East Coast Cyclone

Abstract The role of a diabatically produced lower-tropospheric potential vorticity (PV) maximum in determining the precipitation distribution of the 24–25 January 2000 U.S. East Coast cyclone is investigated. Operational numerical weather prediction (NWP) models performed poorly with this storm, even within 24 h of the event, as they were unable to properly forecast the westward extent of heavy precipitation over the Carolinas and mid-Atlantic. The development of an area of incipient precipitation (IP) around 0600 UTC 24 January over the southeastern United States prior to rapid cyclogenesis was also poorly forecasted by the operational NWP models. It is hypothesized that the lower-tropospheric diabatic PV maximum initially produced by the IP was important to subsequent inland moisture transport over the Carolinas and mid-Atlantic. A PV budget confirms that latent heat release in the midtroposphere associated with the IP led to the initial formation of a PV maximum in the lower troposphere that propagated eastward in association with the IP to the Atlantic coast late on 24 January. The impact of this PV maximum on the westward moisture transport was quantified by piecewise Ertel PV inversion. Results from the inversion show that the balanced flow associated with this evolving cyclonic PV maximum contributed substantially to the onshore moisture flux into the Carolinas and Virginia. The balanced flow associated with the PV anomaly also contributed to quasigeostrophic forcing for ascent in the region. These findings suggest that accurate numerical prediction of the precipitation distribution in this event requires adequate representation of the IP and its associated impacts on the PV distribution.

Microstructure and corrosion behaviour of DC-pulsed plasma nitrided AISI 410 martensitic stainless steel

AISI 410 martensitic stainless steel samples with different metallurgical structures were DC-pulsed plasma nitrided at 623, 723 and 773 K. The samples were ion nitrided in an industrial equipment using a gas mixture consisting of 25% N 2+75% H 2 under a pulsed DC glow discharge. Optical and scanning electron microscopy, as well as glancing angle X-ray diffraction and microhardness measurements have been used to study the ion nitrided surfaces. All plasma nitrided samples showed surface hardness values higher than 1000 HV; the highest value was obtained at 673 K. The case depth was approximately 30 μm for samples nitrided at 673 and 773 K, while the sample nitrided at 623 K showed an ‘expanded ferrite’ phase (α N) and an incipient precipitation of Fe 4N. Depending on the treatment temperature and time, two fronts were formed, termed diffusion front and transformation front; the latter produces a softening of the nitrided case. Electrochemical measurements showed a decrease of corrosion resistance in the samples nitrided during 20 h at 673 and 773 K. Conversely, the sample nitrided at 623 K presented a low corrosion current and more noble corrosion potential.