liyuan sun_electroplating of cr from ionic liquids
TRANSCRIPT
Characterization of Imidazolium Chloride Ionic Liquids Plus Trivalent
Chromium Chloride for Chromium Electroplating Liyuan Sun and Joan F. Brennecke
Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
Results & Discussion
Figure 1. Temperature dependent density of: (A) 1:2 CrCl3·xH2O/[Ch][Cl], (B) 1:2
CrCl3·xH2O/[emim][Cl], (C) 1:2 CrCl3·xH2O/[bmim][Cl], and (D) 1:2 CrCl3·xH2O/[hmim][Cl]
IL Crmetal(at.%) CrOx(at.%)
[Ch][Cl] 70.6 29.4
[emim][Cl] 85.1 14.9
[bmim][Cl] 80.4 19.6
[hmim][Cl] 62.2 37.8
Experimental Structure of ILs used in this study
Choline chloride (ChCl) 1,3-diakyl-imidazolium chloride ionic liquid ([Cnmim]Cl)
(n = 2, 4, 6)
Experimental apparatus for characterization and electroplating
Anton Paar automated microviscometer http://www.paar.ru/files/vyazkost/vizkozimetr
Anton Paar densitometer Solartron electrochemical
impedance interface
Voltammetry and
electroplating cell
Radiometer Analytical
VoltaLab50 potentiostat http://www.radiometer-analytical.com7
Helios Nano Lab Dual Beam
(FEI) SEM/FIB workstation http://www.fei.com/products/dualbeams/helios-
660/?ind=MS
X-Ray Photoelectron
Spectrometer http://mcf.nd.edu/instruments-and-
capabilities/#XPS
Results & Discussion
Figure 2. Arrhenius plots of temperature dependent ionic conductivities
of: (A) 1:2 CrCl3·xH2O/[Ch][Cl], (B) 1:2 CrCl3·xH2O/[emim][Cl], (C)
1:2 CrCl3·xH2O/[bmim][Cl], and (D) 1:2 CrCl3·xH2O/[hmim][Cl]
Figure 3. Arrhenius plots of temperature dependent viscosity of:
(A) 1:2 CrCl3·xH2O/[Ch][Cl], (B) 1:2 CrCl3·xH2O/[emim][Cl], (C)
1:2 CrCl3·xH2O/[bmim][Cl], and (D) 1:2 CrCl3·xH2O/[hmim][Cl]
Figure 4. Walden Plots for different mixtures with same Cr: H2O ratio:
(A) 9H2O/Cr, (B) 12 H2O/Cr, (C) 15 H2O/Cr , and (D) 18 H2O/Cr
Figure 5. Cyclic Voltammograms recorded on glassy carbon electrode
in: (A) 1:2 CrCl3·xH2O/[Ch][Cl], (B) 1:2 CrCl3·xH2O/[emim][Cl], (C)
1:2 CrCl3·xH2O/[bmim][Cl], and (D) 1:2 CrCl3·xH2O/[hmim][Cl]
(υ=20 mV/s, 52 ºC)
Figure 6 (a). XPS spectra of coatings obtained on Cu substrate from
different mixtures: (A) 1:2 CrCl3 ·18H2O/[Ch][Cl], (B) 1:2
CrCl3·18H2O/[emim][Cl], (C) 1:2 CrCl3·18H2O/[bmim][Cl], and (D)
1:2 CrCl3·18H2O/[hmim][Cl] (-2.5 V vs. QRE, 52 ºC, 20 min)
Table 1. Atomic % of different chromium states in coatings
obtained from different mixtures onto Cu substrate.
Figure 6 (b). XPS spectra of coatings obtained from 1:2
CrCl3·18H2O/[bmim][Cl] onto different substrates: (E) brass, and
(F) zinc coated steel (-2.5 V vs. QRE, 52 ºC, 20 min)
lnσ = lnσ0 - EΛ/RT lnη = lnη0 + Eη/RT
Λη = constant
Conclusions
Physicochemical properties, including density, conductivity,
viscosity and ionicity, as well as the electrochemical behavior, of
a series of mixtures based on imidazolium chloride ILs and
chromium(III) chloride have been found to be influenced by the
relative amount of diluent water in the mixtures.
Coatings with comparable or even improved properties have been
successfully obtained through the series of mixtures.
The class of Cr(III)/ILs mixtures could be a promising alternative
to the conventional Cr(VI) containing aqueous baths for
chromium electroplating.
Fig 7(b). SEM image of coatings obtained from 1:2
CrCl3·18H2O/[bmim][Cl] onto : (E) brass and (F) zinc coated steel
Results & Discussion
Figure 7(a). SEM image of coatings on a Cu substrate, from: (A) 1:2
CrCl3·18H2O/[Ch][Cl], (B) 1:2 CrCl3·18H2O/[emim][Cl] (C) 1:2
CrCl3·18H2O/[bmim][Cl] and (D) 1:2 CrCl3·18H2O/[hmim][Cl]
(-2.5 V vs. QRE, 52 ºC, 20 min)
Abstract A series of mixtures consisting of the ionic liquids (ILs) 1-
ethyl-3-methylimidazolium chloride, 1-butyl-3-
methylimidazolium chloride and 1-hexyl-3-methylimidazolium
chloride ([emim][Cl], [bmim][Cl] and [hmim][Cl], respectively)
and trivalent chromium chloride have been prepared.
Physicochemical and electrochemical properties of these
mixtures have been studied and the potential applications of
these mixtures for chromium electroplating, as an alternative to
the conventional hard chromium electroplating processes using hexavalent chromium baths,
have been examined. To optimize the transport properties of the mixtures, different amounts
of ultrapure water were added to the Cr(III) salt-IL mixtures. The physicochemical and
electrochemical properties of the mixtures have been found to be dependent on the relative
water content. Preliminary electroplating results show that these types of Cr(III) salt-IL
mixtures could be promising alternatives to Cr(VI) containing baths for chromium
electroplating applications with the advantage of avoiding the use of highly toxic hexavalent
chromium.
Acknowledgements We acknowledge the National Science Foundation for financial
support for this project. We thank Dr. Aruni Desilva for synthesizing
the [bmim][Cl] and [hmim][Cl] ILs and we thank Daniel Fagnant for
helpful discussions. We thank the Materials Characterization Facilities
(MCF) at Notre Dame for the use of the X-Ray Photoelectron
Spectrometer and we thank the Notre Dame Integrated Imaging
Facility (NDIIF) for the use of the SEM/FIB Workstation. We also
thank Professor Ryan Roeder in the Department of Mechanical
Engineering at Notre Dame for free access to the Vickers hardness
tester.