Electrodeposition of Tantalum

As was shown in Chapter 4, elemental tantalum can be electrodeposited in the water- and air-stable ionic liquid [Pyi,4] TFSA at 200°C using TaFs as a source of tantalum [ 15,16]. The quality of the deposit was found to be improved upon addition of LiF to the deposition bath. At room temperature only ultrathin tantalum layers can be deposited as the element. The electrodeposition of tantalum was investigated by in situ STM to gain insight into the electrodeposition process. 

---

Use of low-temperature molten systems for electrolytic processes related with tantalum and niobium and other rare refractory metals seems to hold a promise for future industrial use, and is currently of great concern to researchers. The electrochemical behavior of tantalum, niobium and titanium in low-temperature carbamide-hilide melts has been investigated by Tumanova et al. [572]. Electrodeposition of tantalum and niobium from room/ambient temperature chloroaluminate molten systems has been studied by Cheek et al. [573],... 

Electrodeposition of tantalum thin layers in the water- and air-stable ionic liquid 1-butyl-l-methyl pyrrolidinium bis (trifluoromethylsulfonyl) amide at 200 °C using TaFs as a source of tantalum is presented in this protocol. The electrodeposition of Ta is not a straightforward process as, under the wrong experimental conditions. Ta subhalides can be formed, see Chapter 4.4. 

The optimum conditions for the electrodeposition of tantalum in molten fluoride were first established by Senderoff and Mellors using the ternary eutectic mixture LiF-NaF-KF (i.e., FLiNaK) with 15 to 40 wt.% K TaF as solute, in an inert atmosphere. 

Stern K.H. and Carlton E.W., Electrodeposition of Tantalum Silicide Coatings from molten salts, (1986),/. Electrochem. Soc., 133, 2157-60. 

Taxil P, Mahenc J (1987) Formatirai of corrosion resistant layers by electrodeposition of relractory metals or by alloy electrowinning in molten fluoride. JAppl Electrochem 17 261-269 Polyakova LP et al (1992) Secondary processes during electrodeposition of tantalum in molten salts. J Appl Electrochem 22 628-637... 

Stem KH, Gadomski ST (1983) Electrodeposition of tantalum carbides from molten salts. J Electrochem Soc 130 300-305 Massot L, Chamelot P, Taxil P (2006) Preparation of tantalum carbide films by reaction of electrolytic carbon coating with the tantalum coating. J Alloys Comp 424(1-2) 199-203... 

Zein El Abedin, S., Welz-Biermann, U., and Endres, F. (2005) A study on the electrodeposition of tantalum on NiTi alloy in an ionic liquid and corrosion behaviour of the coated alloy. Electrochem. Commim, 7(9), 941-946. 

Ispas, A., Adolphi, B., Bund, A., and Endres, F. (2010) On the electrodeposition of tantalum from three different ionic liquids with the bis(trifluoromethyl sulfonyl) amide ion. Phys. Chem. Chem. Phys, 12, 1793-1803. 

The anionic composition of the cathodic product is not the only parameter that can be controlled through electrolysis conditions. Grinevitch et al. [559] reported on the investigation of the co-deposition of tantalum and niobium during the electrolysis of fluoride - chloride melts. Appropriate electrodeposition conditions were found that enable to obtain either pure niobium or alloys. 

S. Senderoff, G. W. Mellors andW. J. Reinhart, The Electrodeposition Of Coherent Deposition Of Refractory Metals The Electrode Reactions In the Deposition Of Tantalum, J. Electrochem. Soc.,... 

Another electrolysis process involves electrodeposition of dense, high-puri-ty tantalum metal. In this electrolysis, electrolyte consists of potassium fluotantalate and potassium fluoride and the anode is made of tantalum upon which electrodeposition from the fused salt occurs. 

The most well-known electrodeposition process from the molten state is that of aluminum, which is deposited from a mixture of AI2O3 in AlF3-NaF at 965 °C. Other commercial processes involving molten salts exist and are exemplified by the deposition of tantalum and zirconium. Processes for Ti deposition from TiCl3 in KCl-LiCl entectics exist. All these escape almost completely97 from the H co-deposition problem of aqueous electrodeposition. 

In this section we will show that air- and water-stable ionic liquids can be used for the electrodeposition of highly reactive elements which cannot be obtained from aqueous solutions, such as aluminum, magnesium and lithium, and also refractory metals such as tantalum and titanium. Although these liquids are no longer air-and water-stable when AICI3, TaFs, TiCU and others are dissolved, quite interesting results can be obtained in these liquids. 

In this chapter we would like to present some plating protocols for the electrodeposition of aluminum, lithium, tantalum and zinc from different ionic liquids. These recipes have been elaborated in our laboratories and should allow the beginner to perform his first electrodeposition experiments. For aluminum we give four different recipes in order to show that the ionic liquid itself can strongly influence the deposition of metals. In the case of tantalum the deposition of the metallic phase is not straightforward as, in unstirred solutions, the more nonstoichiometric tantalum halides form the higher the current density for electrodeposition. Apart from the zinc deposition all experiments should be performed at least under dry air. 

In Chapter 1 we explain the motivation and basic concepts of electrodeposition from ionic liquids. In Chapter 2 an introduction to the principles of ionic liquids synthesis is provided as background for those who may be using these materials for the first time. While most of the ionic liquids discussed in this book are available from commercial sources it is important that the reader is aware of the synthetic methods so that impurity issues are clearly understood. Nonetheless, since a comprehensive summary is beyond the scope of this book the reader is referred for more details to the second edition of Ionic Liquids in Synthesis, edited by Peter Wasserscheid and Tom Welton. Chapter 3 summarizes the physical properties of ionic liquids, and in Chapter 4 selected electrodeposition results are presented. Chapter 4 also highlights some of the troublesome aspects of ionic liquid use. One might expect that with a decomposition potential down to -3 V vs. NHE all available elements could be deposited unfortunately, the situation is not as simple as that and the deposition of tantalum is discussed as an example of the issues. In Chapters 5 to 7 the electrodeposition of alloys is reviewed, together with the deposition of semiconductors and conducting polymers. The deposition of conducting polymers... 

Although many ionic liquids and deep eutectic mixtures based on choline have the advantages to be cheap and no-toxic, they are all hydrophilic and miscible with aqueous solvents. This may be a problem for applications such as the extraction of metal ions from an aqueous phase or the electrodeposition of reactive metals (aluminium, magnesium, tantalum..). 

Cheek GT, De Long HC, Trulove PC (2(XX)) Electrodeposition of niobium and tantalum from a room-temperature molten salt system. Proc Electrochem Soc 99-41 527-533... 

Tantalum Tantalum has unique properties that make it useful for many applications, from electronics to mechanical and chemical systems. Many efforts have been made to develop an electroplating process for the electrodeposition of Ta. High-temperature molten salts were found to be efficient baths for the dectrodepo-sition of refractory metals. To the best of our knowledge, imtil now no successful attempts have been made for Ta electrodeposition at room temperature or even at low temperature in ionic liquids. We present here the first results of tantalum dec-trodeposition in the air and water stable ionic liquid 1-butyl-l-methyl-pyrrolidinium bis(tri-fiuoromethylsulfonyl)amide ([BMP][Tf2N]). 

In addition, ILs could also be used as both solvent and electrolyte for the electrodeposition of copper [35, 36], aluminum [37, 38], tantalum [4], platinum [39], silver [40, 41], gold [40-42], and silicon [43]. For example, Endres et al. have reported the electrodeposition of nanocrystalline metals and alloys, such as aluminum from ILs, which previously could not be electrodeposited from aqueous or organic solutions. This method enabled the synthesis of aluminum nanocrystals with average grain sizes of about 10 nm, Al-Mn alloys, as well as Fe and Pd nanocrystals [4] [as shown in Fig. 4.2). 

RuO -embedded PANI electrodes, prepared by the electrodeposition of PANI on tantalum sheet followed by RuO particles embedding on PANI film and final annealing of PANI/RuO electrode at 80 C for 12 h, showed high specific capacitance (474 F g ). ideal cycling stabihty, and small charge-transfer resistance (2.24 O) [237]. Supercapacitor electrodes based... 

Horizons Titanium Corporation, U.S. A. Fused Salt Bath for the Electrodeposition of the Polyvalent Metals Titanium, Tantalum and Vanadium. British Patent 791,151 (1958). 

Wainer, E. (1959) Transition-metal hahdes for electrodeposition of transition metals. US Patent 2,894,886. Timax Corp. (1960) Electrolytic preparation of pure niobium and tantalum. British Patent 837,722. 

Chamelot P., Taxil P. and Lafage B., Voltammetric studies of tantalum electrodeposition baths, (1994), Electrochemica Acta, 39, 2571-75. 

Impurity analysis of tantalum powder Joint electrodeposition of niobium-tin... 

---