Electrodeposition and Characterization of Manganese Coatings

Abstract

Manganese coatings of high quality are electrodeposited on steel substrates from simple sulfate solutions with addition of ammonium sulfate. Potentiodynamic scans and galvanostatic experiments are used to study manganese electrodeposition in a wide range of pH and current density. The effect of these variables on the microstructure, crystallography, mechanical, and corrosion-resistance properties of manganese deposits are investigated. It is found that ammonium sulfate enhances the reduction reaction of the manganese ion and provides a buffering effect. Two types of manganese deposits can be obtained depending on current density: crystalline films (type I, body-centered tetragonal γ-Mn) at low current density and amorphous films (type II) at high current density. Bright manganese films with (002) preferential orientation are electrodeposited at low pH. Type I structures show recrystallization at room temperature with phase transformation; the rate of phase transformation from γ-Mn to α-Mn (body-centered cubic) follows a Johnson-Mehl-Avrami kinetics. Crystalline films obtained at relatively high current density and low pH tend to have higher phase transformation rates. Amorphous films show good corrosion resistance both in acidic sodium sulfate/borate and sodium chloride electrolytes. © 2002 The Electrochemical Society. All rights reserved.

Electrodeposition and characterization of sacrificial copper-manganese alloy coatings: Part II. Structural, mechanical, and corrosion-resistance properties

“…This is probably a consequence of the increased hydrogen evolution and incorporation in the coating during electrodeposition at low pH. Similar to Mn electrodeposition, [1,26] where the incorporation of interstitial hydrogen enlarges the lattice, here it is reasonable to assume that Cu-Mn coatings are always saturated with hydrogen and that the extra expansion of the lattice compared with the cast alloy with a low Cu content is due to the hydrogen incorporation. The lattice expansion due to hydrogen incorporation can be estimated from Figure 4 to be in the range 0.01 to 0.03 Å.…”

“…This transformation kinetics was closely obeyed in electrodeposited Mn. [1] Figure 6 shows the recrystallization kinetics for electrodeposited Mn, Cu 1.9 Mn 98.1 , Cu 2.7 Mn 97.3 , and Cu 3.9 Mn 96.1 in linearized form, log 10 ln (1/(1 Ϫ f )) vs log 10 t. A higher Cu content increases the c/a ratio and preserves the ␥Ј phase for a longer time. No phase transformation has been, in fact, discerned for Cu 5.2 Mn 94.8 coatings for more than 2.5 years.…”

“…Pure Mn coatings on steel, however, are highly reactive and exhibit a high corrosion current and quick dissolution. [1,2] Alloying of Mn with other metals such as zinc, [3][4][5][6][7][8] nickel, [9,10] iron, [11,12] chromium, [13] cobalt, [14] or tin [15] potentially enables tailoring of the corrosion potential and dissolution kinetics, improving the coating performance. Ideal sacrificial coatings should provide, in addition, suitable contact and soldering surfaces for any foreseeable application in the field and, therefore, should exhibit a low friction coefficient, low ductility, good electrical conductivity, and good solderability both at the nano-and microscale, where surface interactions will occur.…”

“…[1,2] This ductile metastable phase undergoes room-temperature recrystallization to a brittle bcc ␣ phase in a time frame of several weeks, which easily leads to cracking and flaking upon impact or abrasion and should be prevented or retarded. Cu additions to Mn, in particular, can stabilize electrodeposited Mn in its ductile form [2] and, potentially, could tune the redox potential of the alloy, thus allowing control of the dissolution kinetics.…”

Manganese electrodeposition from urea-rich electrolyte

“…Namely, it is known that [Cr(H 2 O) 5 complexes which are reduced more easily [22,23]. Therefore, the observed influence of urea on Mn reduction in this work could be explained through the formation of complex salts like [Mn(urea) 3 2+ which are well documented [24]. On the contrary, the role of 8 mol dm -3 urea in increasing the rate of HER is not easy to explain and it requests further research, also because we could not find any report regarding the catalytic or inhibiting activity of urea towards water reduction.…”