Microscopic investigations of electrochemical machining of Fe in NaNO3

Lohrengel, M. M.; Klüppel, Ingo; Rosenkranz, C.; Bettermann, H.; Schultze, J.W.

doi:10.1016/s0013-4686(03)00372-4

Cited by 122 publications

(87 citation statements)

References 16 publications

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“…This is the first reported crystal structure of ferrous nitrate. The salt layer is also found to give an anisotropic diffraction pattern, consistent formation of platelets with (0 2 0) It is well known that salt layers can form at the bottom of growing corrosion pits due to supersaturation of metal salts, [1][2][3][4] and that the presence of salt layers is important for continued pit growth.5 This information is significant both in the field of electrochemical machining (ECM), where nitrate solutions are often used, [6][7][8] and in corrosion of steel in radioactive waste solutions. …”

mentioning

confidence: 78%

In-situ Synchrotron Studies of the Effect of Nitrate on Iron Artificial Pits in Chloride Solutions

Street

Amri

et al. 2015

J. Electrochem. Soc.

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The effect of nitrate on the salt layers in iron artificial corrosion pits in acidic chloride solutions has been studied using in-situ synchrotron X-ray diffraction. During dissolution in 1 M HCl, there is a salt layer of FeCl 2 .4H 2 O on the electrode surface, which is isotropic. With addition of trace nitrate, the salt layer remains FeCl 2 .4H 2 O and no nitrate phase is observed, but the diffraction pattern becomes anisotropic, consistent with the formation of platelets with (1 2 0) planes settling horizontally. In nitrate solution containing trace of chloride (0.1 M HNO 3 + 10 mM HCl), a salt layer is formed that is isostructural with Co(NO 3 ) 2 .6H 2 O, and therefore assumed to be Fe(NO 3 ) 2 .6H 2 O. This is the first reported crystal structure of ferrous nitrate. The salt layer is also found to give an anisotropic diffraction pattern, consistent formation of platelets with (0 2 0) It is well known that salt layers can form at the bottom of growing corrosion pits due to supersaturation of metal salts, [1][2][3][4] and that the presence of salt layers is important for continued pit growth.5 This information is significant both in the field of electrochemical machining (ECM), where nitrate solutions are often used, [6][7][8] and in corrosion of steel in radioactive waste solutions. 9-11These salt layers are a slurry of crystallites that form on a dissolving metal surface 12 when the rate of metal ion production (dissolution) is greater than the rate that they can diffuse from the interface, leading to supersaturation and thus crystallite nucleation. The equilibrium thickness of the layer is determined by a self-regulating process.

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mentioning

confidence: 78%

In-situ Synchrotron Studies of the Effect of Nitrate on Iron Artificial Pits in Chloride Solutions

Street

Amri

et al. 2015

J. Electrochem. Soc.

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“…This process, however, is not an electrochemical process, meaning it is a chemical reaction that will happen regardless of a current being passed and it does not occur at the electrode surface. 2,5,29,30 The total current passed is not affected by this reaction. Figure 3 schematically shows the processes occurring during ECM of an iron workpiece in sodium nitrate.…”

Section: Process Overviewmentioning

confidence: 95%

Electrochemical micromachining: An introduction

Leese

Ivanov

2016

Advances in Mechanical Engineering

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Electrochemical machining is a relatively new technique, only being introduced as a commercial technique within the last 70 years. A lot of research was conducted in the 1960s and 1970s, but research on electrical discharge machining around the same time slowed electrochemical machining research. The main influence for the development of electrochemical machining came from the aerospace industry where very hard alloys were required to be machined without leaving a defective layer in order to produce a component which would behave reliably. Electrochemical machining was primarily used for the production of gas turbine blades or to machine materials into complex shapes that would be difficult to machine using conventional machining methods. Tool wear is high and the metal removal rate is slow when machining hard materials with conventional machining methods such as milling. This increases the cost of the machining process overall and this method creates a defective layer on the machined surface. Whereas with electrochemical machining there is virtually no tool wear even when machining hard materials and it does not leave a defective layer on the machined surface. This article reviews the application of electrochemical machining with regards to micro manufacturing and the present state of the art micro electrochemical machining considering different machined materials, electrolytes and conditions used.

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“…The surface is suddenly passivated at approximately 1.6 V and the current density decreases to nearly 0 A cm -2 , oxygen evolution starts at 1.8 V and transpassive dissolution sets in at higher current densities. With respect to the models of metal/electrolyte interface [11,14,16] the following mechanistic model can be proposed. At lower current densities which occur at potentials below 1.6 V at the resting electrode, the dissolution mechanism must be dominated by the chloride anions and the LSV is very similar to the curve in pure chloride solution.…”

Section: Sharp Transition From Active To Transpassive Dissolution At mentioning

confidence: 99%

“…Qualitative anodic dissolution models explain the observed dissolution behaviour and the resulting surfaces. A two-layer model explains the dissolution in nitrate electrolyte [8,15,16]. Because of the current density-dependent divalent/trivalent dissolution of iron, different iron oxides (Fe 2 O 3 and Fe 3 O 4 ) are formed and cover the steel surface as a thin film.…”

Section: Introductionmentioning

confidence: 99%

“…Because of the current density-dependent divalent/trivalent dissolution of iron, different iron oxides (Fe 2 O 3 and Fe 3 O 4 ) are formed and cover the steel surface as a thin film. An adherent liquid polishing film consisting of supersaturated iron nitrate hydrates is built at the oxide/electrolyte interface and causes a decreasing oxygen evolution rate [11,16]. In chloride media a weakly attached, easily removable black, carbide-rich solid surface film and a thin polishing film consisting of FeCl 2 , Fe(OH) 2 and FeO (Fe x O y Cl z ) are formed at the active-steelanode/electrolyte interface [14].…”

Section: Introductionmentioning

confidence: 99%

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