Tantalum electrodeposition

Platinum electrodeposition on to tantalum had been carried out as early as 1913 and the use of platinised tantalum as an anode suggested in 1922 , whilst platinum electrodeposition on to niobium was first successfully carried out in 1950 . 

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. 

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],... 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

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.,... 

Anodic electrodeposition (AED), 10 448 Anodic electrodeposition coatings, 10 381 Anodic inhibitors, 7 815 Anodic oxidation, on tantalum, 24 327—330 Anodic oxidation waste treatment, 9 643 Anodic oxide films... 

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. 

Between 1980 and about 2000 most of the studies on the electrodeposition in ionic liquids were performed in the first generation of ionic liquids, formerly called room-temperature molten salts or ambient temperature molten salts . These liquids are comparatively easy to synthesize from AICI3 and organic halides such as Tethyl-3-methylimidazolium chloride. Aluminum can be quite easily be electrode-posited in these liquids as well as many relatively noble elements such as silver, copper, palladium and others. Furthermore, technically important alloys such as Al-Mg, Al-Cr and others can be made by electrochemical means. The major disadvantage of these liquids is their extreme sensitivity to moisture which requires handling under a controlled inert gas atmosphere. Furthermore, A1 is relatively noble so that silicon, tantalum, lithium and other reactive elements cannot be deposited without A1 codeposition. Section 4.1 gives an introduction to electrodeposition in these first generation ionic liquids. 

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. 

Recently, we reported for the first time that tantalum can be electrodeposited as 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 [88]. The quality of the deposit was found to be improved on addition of LiF to the... 

In these clusters tantalum atoms are bound to other tantalum atoms and are also edge bridged via halide. As our deposit was completely amorphous without any XRD peak we concluded that it did not consist of crystalline tantalum but rather of such clusters. We varied the electrode potential for deposition and tried deposition with very low constant current densities, but in no case was crystalline tantalum obtained. Thus, the electrochemical window of our liquid was surely wide enough, but for some reason the electrodeposition stopped before Ta(0) was obtained. When we studied the literature dealing with metal clusters we found that the cluster chemistry with fluoride seems to be less comprehensive. Consequently... 

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... 

Electrodeposition is one of a few techniques used to crystallize high-melting materials at convenient temperatures [e.g., tantalum carbide, TaC (mp 3900°C) and niobium carbide, NbC (mp 3500°C) are crystallized at 750°C]. The preparation involves electrolysis of melts containing Ta20s (or Nb205), Na2B407, Na2C03, NaF, and KF. 

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... 

The preconcentration of metals by electrodeposition onto a tantalum strip for flameless AAS has not been described and though similar to the wire-loop atomizer, the greater stability and malleability attainable with tantalum should make it possible to extend the method more readily to other metals. In fact, the... 

Dissolve the salt in 1 ml of water and transfer to the electrodeposition cell fitted with a tantalum disk. Add 4 ml of 6 N NH Cl solution and 2 drops of concentrated HCl. 

Electrodeposit at 2.5 to 3.0 A for 20 min. Quench the cell with 1 ml of concentrated NH OH. Wash the solution from the cell with distilled water and dry the tantalum disk on a hot plate. 

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