Journal of Applied Electrochemistry, 2008

This work presents a study of a hard chromium plating process using low concentration H 2 CrO 4 baths. In particular, the effect of different values of CrO 3 /H 2 SO 4 ratio on coating properties such as adhesion, hardness, surface roughness, apparent density and microstructure were considered. To increase the solution conductivity, avoiding long deposition times and low throwing power typical of dilute solutions, the behaviour of various inorganic compounds was investigated. Specifically, the compounds suitable for obtaining brighter coatings with lower surface roughness values than those obtained using Fink's solutions were Na 2 SO 4 and Al 2 (SO 4 ) 3 9 18H 2 O. A bath composition was identified, with a limited use of Cr(VI) in a solution able to produce coatings with a better surface roughness than those of conventional industrial baths.

Modelado de la biodegradación en biorreactores de lodos de hidrocarburos totales del petróleo intemperizados en suelos y sedimentos (Biodegradation modeling of sludge bioreactors of total petroleum hydrocarbons weathering in soil and sediments)

Electrochimica Acta, 2010

Amorphous chromium coatings were electrodeposited from Cr(III)-based solutions containing organic (HCOONa) or phosphorus-containing (NaH 2 PO 2) additives. Their structure was studied by a combination of X-ray diffraction (XRD), valence-to-core X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) at the Cr K-edge. Metalloid atoms (C or P) incorporated in electroplates structure are chemically bonded to chromium (i.e. are located in the first coordination shell). Upon annealing at elevated temperatures in vacuum, these amorphous coatings crystallize into a mixture of phases containing metallic chromium and chromium carbides or chromium phosphides. Quantitative analysis of valence-to-core XES data demonstrates that the average local structure of chromium in the amorphous coatings does not change significantly during crystallization.

Electrochimica Acta, 2018

The reduction mechanism of Cr(III) depends on the nature of the complexing agent present in electroplating solutions. In pure water solutions and without any other additives, Cr (III) is complexed with water molecules, creating a stable [Cr(H 2 O) 6 ] 3+ complex. [Cr(H 2 O) 6 ] 3+ can be reduced to Cr(0) in two steps via a chromium(II) intermediate species. However, this reduction is not quantitative, and the Cr(0) coating is difficult to grow. The destabilization of the [Cr(H 2 O) 6 ] 3+ complex via the addition of an organic complexing agent allows the formation of a reducible Cr(III) complex. The different complexes obtained with the addition of oxalate, formate or acetate were characterized by UV-visible spectroscopy and HPLC-ICP/AES. The nature of the ligand, the [Cr]/[L] ratio and the pH of the solution influence the chemical mechanism of the Cr(III) reduction. Independently of the complex nature, the reduction of Cr(III) to Cr(0) occurs in one step with the three studied complexing agent. Moreover a more quantitative reduction can be obtained by using an organic complexing agent, low [Cr]/[L] ratios and a pH of approximately 3.5.

Electrochimica Acta, 2009

Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solutions is shown to proceed via the formation of relatively stable intermediates-Cr(II) compounds which are partially removed into bulk solution. The effect of pH, organic ligand concentration and disk rotation velocity on the partial current density of chromium electroplating was demonstrated. The kinetic equations of the studied process were derived and compared with the experimental data. Kinetic parameters for the discharge of Cr(II) ions were calculated. The mechanism of chromium electrodeposition reaction was proposed. The electrodeposition of chromium from formate bath is suggested to proceed with the participation of hydroxocomplexes of bivalent chromium. The oxalate complexes of bivalent chromium directly discharge in the electrolytes containing oxalic acid. The partial polarization curves of chromium electrodeposition exhibit a current peak which may be caused by blocking the electrode surface with poorly soluble Cr(III) hydroxide.

Transactions of the IMF, 1999

Electrodeposition of Thick Chron1iun1 Coatings fron1 an Environn1en tally Acceptable Chron1iun1 (111)-Glycine Complex SUMMARY-Hexavalent chromium process provides unique engineering coatings in terms of wear and corrosion resistance. However, this process is under pressure due to its environmentally unfriendly attributes. Recently significant advances have been made on the development of an electrolyte based on chromium(III)glycine complex. A successful enhancement of both quality of deposits and the rate of deposition has been achieved using high speed and conventional techniques. A clear correlation has been established between the percentage chromium metal deposited and the formation of chromium(/I I)-glycine complexes leading to the identification of the species suitable for chromium deposition.

Thin Solid Films, 2011

In the present study, black chromium coatings were electrodeposited from a 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF 4 ]) solution containing Cr(III) under potentiostatic control on copper substrates. The electrochemical behavior of the electrolyte was studied by cyclic voltammetry. The reduction of Cr(III) species in the solution is a two-step process, from Cr(III) to Cr(II) and from Cr(II) to Cr(0). The potential of each reaction shifts positively with the increase of the electrolyte temperature. The parameters for the electrodeposition of black chromium films were optimized. Homogeneous black chromium films with spectrally selective optical properties were produced by applying a potential of −1.5 V for 1800 s, at an electrolyte temperature of 85°C. The coatings consist of a mixture of chromium oxide/hydroxide and metallic chromium. They are amorphous and present a sub-micrometric granular structure.

Metal Finishing, 2011

Effect of bath composition and electrolysis conditions on the current efficiency, electroplating rate and surface morphology ofCr-coatings was studied using a trivalent chromium bath containing chromium sulfate, sodium sulfate, aluminium sulfate, boric acid, formic acid, carbamide and surfactant. The optimal concentrations of Cr(II1)ions, carbamide and formic acid were stated to be 1.0, 0.5 and 0.5 M, respectively. At optimal bath composition and electrolysis conditions, the deposition rate does not appreciably diminish during electrolysis time and reaches -1-1.5 J.l.m min'l. The value ofcurrent efficiency of chromium electrodeposition process is close to -30-40%. The thick chromium coatings deposited from the bath under consideration are bright and smooth; they exhibit nodular rype of surface structure.

Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solutions is shown to proceed via the formation of relatively stable intermediates-Cr(II) compounds which are partially removed into bulk solution. The effect of pH, organic ligand concentration and disk rotation velocity on the partial current density of chromium electroplating was demonstrated. The kinetic equations of the studied process were derived and compared with the experimental data. Kinetic parameters for the discharge of Cr(II) ions were calculated. The mechanism of chromium electrodeposition reaction was proposed. The electrodeposition of chromium from formate bath is suggested to proceed with the participation of hydroxocomplexes of bivalent chromium. The oxalate complexes of bivalent chromium directly discharge in the electrolytes containing oxalic acid. The partial polarization curves of chromium electrodeposition exhibit a current peak which may be caused by blocking the electrode surface with poorly soluble Cr(III) hydroxide.

Protection of Metals and Physical Chemistry of Surfaces, 2013