Film formation in trihexyl(tetradecyl)phosphonium diphenylphosphate ([P6,6,6,14][dpp]) ionic liquid on AA5083 aluminium alloy

Whilst ionic liquids (IL) have been shown to inhibit corrosion on some reactive metals and alloys by forming a surface film, e.g. Li and Mg, understanding of the interaction between ionic liquids and aluminium is lacking. This research study investigated the viability of film formation on AA5083 Aluminium Alloy by electrochemical treatments in the trihexyl(tetradecyl)phosphonium diphenylphosphate ([P6,6,6,14][dpp]) IL. Two-step anodic treatments were performed on AA5083 in the IL, followed by a comparison of the corrosion behaviour of the IL-treated samples with that of a control. It has been revealed that the two-step IL-treatment led to reduced current densities on AA5083 under cyclic voltammetry scan in the IL before and after the IL-treatment. Lower corrosion rates have been shown on all samples treated in IL at room temperature. Surface characterisation showed a non-uniform porous film on the 50°C IL-treated sample with a film thickness ranging between 37nm and 155nm. The IL-film enhanced the corrosion resistance of AA5083 by protecting the Al-matrix and Fe-rich intermetallic particles (IMPs). Although findings of this study suggest similar IL-film formation as that on Li and Mg, more research needs to be conducted to optimise the electrochemical treatment conditions and ultimately to develop a robust IL-film formation procedure for corrosion protection.

Synthesis and physical property characterisation of phosphonium ionic liquids based on P(O)2(OR)2− and P(O)2(R)2− anions with potential application for corrosion mitigation of magnesium alloys

Phosphonium cation based ionic liquids (ILs) have become of interest due to their unique chemical and electrochemical stability as well as their promising tribological properties. At the same time, interest has also grown in the use of phosphate and phosphinate based ionic liquids for corrosion protection of reactive metals. In this work we describe the synthesis and characterization of six novel ionic liquids based on the tetraalkylphosponium cation coupled with organophosphate and organophosphinate anions and their sulfur analogues. The conductivity and viscosity of these ILs has been measured and discussed in terms of the nature of the interactions, effect of anion basicity and the extent of ionic character. The reaction of the IL with a ZE41 magnesium aerospace alloy surface is also demonstrated.

The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys

An electrochemical approach to the formation of a protective surface film on Mg alloys immersed in the ionic liquid (IL), trihexyl(tetradecyl)phosphonium–bis 2,4,4-trimethylpentylphosphinate, was investigated in this work. Initially, cyclic voltammetry was used with the Mg alloy being cycled from OCP to more anodic potentials. EIS data indicate that, under these circumstances, an optimum level of protection was achieved at intermediate potentials (e.g., 0 or 0.25 V versus Ag/AgCl). In the second part of this paper, a small constant bias was applied to the Mg alloy immersed in the IL for extended periods using a novel cell design. This electrochemical cell allowed us to monitor in situ surface film formation on the metal surface as well as the subsequent corrosion behaviour of the metal in a corrosive medium. This apparatus was used to investigate the evolution of the surface film on an AZ31 magnesium alloy under a potential bias (between ±100 mV versus open circuit) applied for over 24 h, and the film evolution was monitored using electrochemical impedance spectroscopy (EIS). A film resistance was determined from the EIS data and it was shown that this increased substantially during the first few hours (independent of the bias potential used) with a subsequent decrease upon longer exposure of the surface to the IL. Preliminary characterization of the film formed on the Mg alloy surface using ToF-SIMS indicates that a multilayer surface exists with a phosphorous rich outer layer and a native oxide/hydroxide film underlying this. The corrosion performance of a treated AZ31 specimen when exposed to 0.1 M NaCl aqueous solution showed considerable improvement, consistent with electrochemical data.

Ionic liquid pretreatment as a means to control the corrosion behavior of magnesium alloys in simulated body fluid

Recently, the use of magnesium alloys as metallic implant materials for biodegradable coronary artery stents has been steadily growing in interest. However, AZ31 magnesium alloys present poor corrosion resistance in the body environment. This work reports on the use of a treatment with low-toxicity IL Trimethyl (butyl) phosphonium diphenyl phosphate P₁₄₄₄DPP, which provides corrosion protection for magnesium alloy AZ31 in simulated body fluid (SBF). Before IL treatment, surface was cleaned by HNO₃ and H₃PO₄ acid pickling solution. The effect of ionic liquid treatment on the corrosion performance of magnesium alloys AZ31in simulated body fluid has been investigated by electrochemical tests and the observation of surface morphology. The results show that this IL treatment succeeded in increasing the corrosion resistance of AZ31 when exposed to SBF.

Studies on the structural and ionic transport properties at elevated temperatures of La1-xMnO3 +/-delta synthesized by a wet chemical method

Structural transformation and ionic transport properties are investigated on wet-chemically synthesized La1-xMnO3 (X=0.0-0.18) compositions. Powders annealed in oxygen/air at 1000-1080 K exhibit cubic symmetry and transform to rhombohedral on annealing at 1173-1573 K in air/oxygen. Annealing above 1773 K in air or in argon/helium at 1473 K stabilized distorted rhombohedral or orthorhombic symmetry. Structural transformations are confirmed from XRD and TEM studies. The total conductivity of sintered disks, measured by four-probe technique, ranges from 5 S cm(-1) at 298 K to 105 S cm(-1) at 1273 K. The ionic conductivity measured by blocking electrode technique ranges from 1.0X10(-6) S cm(-1) at 700 K to 2.0X10(-3) S cm(-1) at 1273 K. The ionic transference number of these compositions ranges from 3.0X10(-5) to 5.0X10(-5) at 1273 K. The activation energy deduced from experimental data for ionic conduction and ionic migration is 1.03-1.10 and 0.80-1.00 eV, respectively. The activation energy of formation, association and migration of vacancies ranges from 1.07 to 1.44 eV. (C) 2002 Elsevier Science B.V. All rights reserved.

Study on structure and oxide ionic conductivity for new compound Ce(6-x)Ln(x)MoO(15-delta)

A new compound Ce(6-x)Ln(x)MoO(15-delta) has been synthesized by wet-chemistry method. Their crystal structure and oxide ionic conductivity were characterized by powder X-ray diffraction, Raman, IR spectrum and A.C. impedance technique. The XRD results showed that Ce6MO15-delta, Ce(5)LnMoO(15-delta) have cubic symmetry with Fm3m space group. The refined lattice parameters showed that their lattice constants decrease with the decrease of the ionic radius of Ln(3+). The electrochemical measurements showed that the ionic conductivity of resulting oxides Ce(6-x)Ln(x)MoO(15-delta) have an enhance, which may be a kind of promising material for SOFCs.

Remarkable stability of ionic gold supported on sulfated lanthanum oxide

Isolated cationic gold deposited on sulfated lanthanum oxide has been shown to exhibit remarkable stability opening a promising way of stabilising ionic gold for catalytic reactions.

Hydrophobic ionic liquids with strongly coordinating anions

Ionic liquids containing the hexafluoroacetylacetonate anion are immiscible with water and they exhibit strong metal-complexing ability.

On the dissolution of non-metallic solid elements (sulfur, selenium, tellurium and phosphorus) in ionic liquids

Ionic liquids are shown to be good solvents for elemental sulfur, selenium, phosphorus and tellurium, and can be designed to maximise the solubility of these elements. The presence of the [S-3](center dot-) radical anion in diluted solutions of sulfur in some ionic liquids has been confirmed, and is the origin of their intense blue colour (cf. lapis lazuli).

Overcoming hydrolytic sensitivity and low solubility of phosphitylation reagents by combining ionic liquids with mechanochemistry

Ionic liquids have been used in combination with ball milling on a range of chlorophosphoramidite reagents to phosphitylate nucleosides and 2-deoxynucleosides. The enhanced stability offered by the ionic liquid mediated processes combined with efficient mass transfer induced by ball milling has enabled excellent yields to be obtained even when using small dialkyl amino groups as well as the more commonly used diisopropylamino protection.

Reaction of elemental chalcogens with imidazolium acetates to yield imidazole-2-chalcogenones: direct evidence for ionic liquids as proto-carbenes

Mechanistic analysis of the reaction between elemental sulfur or selenium and 1,3-dialkylimidazolium acetate ionic liquids, in the absence of an external base or solvent, affords evidence for the equilibrium presence of carbene species in these ionic liquids. It demonstrates the potential to control, through anion selection, the concentration of carbene in stable ionic liquids.

Phosphine oxide functionalised imidazolium ionic liquids as tuneable ligands for lanthanide complexation

A series of novel, phosphine oxide functionalised ionic liquids have been synthesised and their application as tuneable lanthanide complexing agents is demonstrated.

Determining relative rates of cellulose dissolution in ionic liquids through in situ viscosity measurement

Using in situ viscosity measurement, the rate of cellulose dissolution in a number of ionic liquids has been determined allowing their performance as solvents to be quantitatively assessed. 1-Butyl-3-methylimidazolium ethanoate was shown to dissolve cellulose faster than analogous ionic liquids with chloride or dimethylphosphate anions. Analysis of the data highlights the influence of both anion basicity and relative concentration on the rate of dissolution.

Tuning solute redox potentials by varying the anion component of room temperature ionic liquids

The electrode potentials for the two one electron oxidations of 1,2-diferrocenylethylene (bisferrocene, BF) were studied relative to that of the one electrode oxidation of decamethylferrocene in a variety of RTILs. The difference in these potentials was found to be very sensitive to the anion component of the ionic liquid showing the scope of these solutes as 'designer media' to tune the thermodynamic properties of solutes dissolved in them.