Troublesome Aspects

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 

The cyclic voltammogram is quite similar to the voltammogram of TaCls and consists mainly of two reduction processes. There is no visible surface process at 

It is known in inorganic chemistry that all refractory and rare earth elements tend to form subvalent halides from their iodides, bromides and chlorides. 

In the case of tantalum deposition the addition of LiF was required. On the one hand the Li+ ion might destabilize the Ta-F bond and thus facilitate the deposition of tantalum, on the other hand Li+ ions might influence the electrochemical double layer and facilitate charge transfer. We are about to perform in situ STM studies, the results will be reported in the peer reviewed literature. 

Mass transport may influence material growth in ionic liquids. 1-Butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, for example, is, at room temperature, about 60 times more viscous than water. At temperatures above 150°C its viscosity is similar to most molecular solvents at ambient conditions. Indeed, temperatures between 150 and 200 °C were best to deposit tantalum from TaFs in the presence of LiF. One has to keep in mind that the deposition of tantalum from TaFs or an anionic complex delivers one Ta atom and 5-7 fluorides. If the deposition is too fast F may not diffuse rapidly enough from the surface to the bulk of the solution and may be trapped in the deposit. This might explain why we only got crystalline tantalum layers at low current densities. 

---

Another troublesome aspect of the reactivity ratios is the fact that they must be determined and reported as a pair. It would clearly simplify things if it were possible to specify one or two general parameters for each monomer which would correctly represent its contribution to all reactivity ratios. Combined with the analogous parameters for its comonomer, the values rj and t2 could then be evaluated. This situation parallels the standard potential of electrochemical cells which we are able to describe as the sum of potential contributions from each of the electrodes that comprise the cell. With x possible electrodes, there are x(x - l)/2 possible electrode combinations. If x = 50, there are 1225 possible cells, but these can be described by only 50 electrode potentials. A dramatic data reduction is accomplished by this device. Precisely the same proliferation of combinations exists for monomer combinations. It would simplify things if a method were available for data reduction such as that used in electrochemistry. 

Unsaturated Group Reactions. In addition to a comprehensive review of these reactions (16), there are excellent texts (17,18). Free-radical-initiated polymerization of the double bond is the most common reaction and presents one of the more troublesome aspects of monomer manufacture and purification. 

Micro-pipetting instruments such as the "Eppendorf or "Oxford pipettors with disposable plastic cone tips are customarily employed to dispense the liquid samples into electrothermal atomizers. Sampling problems which are associated with the use of these pipettors are among the troublesome aspects of electrothermal atomic absorption spectrometry (67,75). The plastic cone-tips are frequently contaminated with metals, and they should invariably be cleaned before use by soaking in dilute "ultra pure nitric acid, followed by multiple rinses with demineralized water which has been distilled in a quartz still. 

The use of an anionic reagent for addition at carbonyl carbon rather than a fully esterified form of a trivalent phosphorus acid obviates a troublesome aspect of the Abramov reaction. Specifically no dealkylation step is required. Mechanistic investigations257 258 indicate that the reaction proceeds much as a simple "aldol"-type reaction in which the anionic phosphorus site adds directly to the carbonyl center. While the initial efforts concerned with the "Pudovik reaction"259 were directed toward the use of sodium salts of the simple dialkyl phosphites, as shown in Equation 3.17,260 266 with a, 5-unsaturated carbonyl systems (vide infra) competition between sites for addition can occur. Addition at the carbonyl carbon site is the kinetically favored route.267-270... 

Concern about this troublesome aspect of the behavior of scientists acting as technical advisers and decision makers was expressed by the same former Commissioner of Food and Drugs in the context of regulating carcinogenic substances in the environment. He stated(3d) ... 

The behavioral and emotional complications of dementia such as agitation, depression, and psychosis are often the most troublesome aspect of the illness. They can alienate the family members who are trying to provide care and often lead exhausted families to institutionalize these patients whom they would otherwise prefer to keep at home. 

In the study of work-function changes of metals caused by the presence of adsorbates, the most troublesome aspect is that of obtaining a sufficiently well-defined surface. There is considerable experimental evidence based on... 

Lee s progress through the detoxification was uneventful, with poor sleep the most troublesome aspect. He was pleasantly surprised with the low level of withdrawal discomfort, compared to his own attempts to come off heroin without medication. He and his parents followed the instructions carefully, and in all Lee used about three-quarters of the available medication, apart from the sleeping tablets, which were all necessary. Nine days after his last use of heroin naltrexone was instituted, with no withdrawal reaction. 

A troublesome aspect still to be considered is the observation that salicylanil undergoes amine exchange, though 4-phenyliminopentane-2-one does not. Probably, this is due to the difference in resonance stabilization of the two compounds... 

One troublesome aspect of solving low-speed flow problems numerically is dealing with the hyperbolic characteristics of pressure waves. Since the pressure waves usually have no importance in these problems, they are mainly a mathematical and computational nuisance. Therefore techniques to filter pressure waves are often desirable. The stream-function-vorticity approach accomplishes this filtering, but it is not now used very much... 

In Section 4.4, finally, troublesome aspects are shortly summarized. An important aspect is that the electrochemical window alone is not sufficient and one can be pretty surprised if the electroreduction of e.g. TaCls rather delivers non-stoichiometric halides instead of the desired tantalum metal. For an electroplating bath the solution chemistry also plays an important role and a new concept of additives seems to be necessary. 

The motivation of this chapter was to show that despite the enormous prospects of ionic liquids in electrodeposition some troublesome aspects have to be expected. Apart from the purity and price of ionic liquids the optimum temperature for any process has to be found. Furthermore, suitable additives for electrodeposition will have to be developed and cation/anion effects that can strongly alter the morphology of deposits have to be expected. Finally, the electrochemical window alone is not the only factor that needs to be considered for the deposition of reactive metals. Suitable precursors will have to be tailor-made and it is our personal opinion that the electrodeposition of metals like Mg, Ti, Ta and Mo may not be possible from metal halides but rather metal bis(trifluoromethylsulfonyl)amide salts and other ones may be more suitable. 

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... 

Adding the data to the scaled plot is the least troublesome aspect of the task and can be handled easily by most plotting programs as well as people. 

One of the most troublesome aspects of isoelectric focusing is how to modulate the slope of the pH gradient to increase resolution (equivalent to pH gradient engineering, as easily available in immobilized pH gradients). A simple solution is offered with addition, to the standard 2-pH-units interval, of separa-... 

The use of MBI for LC-MS stopped, because it is a complex mechanical device, requiring high operating skills. Renewal of the belt and belt memory are troublesome aspects as well. The MBI application field was taken over by the particle-beam interface (Ch. 4.8). 

Contrasting with this troublesome aspect, the lack of conservation of the wrapping (dehydron) pattern across kinases has paramount potential to promote drug specificity, as illustrated in Fig. 7.1c, d. Thus, the structural alignment of the focal adhesion kinase (FAK, PDB.2J0L) and the insulin receptor kinase (PDB.1GAG)... 

Perhaps the most troublesome aspect of batch crystallizers is the difficulty associate ciystal size distributions in going from one batch to the next. This may be overcome and control of mixing conditions. In general, however, the development of methods for design and analysis of batch crystallizers lags those for cortinuous systems. 

A troublesome aspect of Fig. 41 is the low standard reduction potential of the hydrogen couple at the right. By the criterion of standard potentials, C3 should not be able to donate electrons to H. But these standard potentials assume equal amounts of reduced and oxidized C3, at pH 7, and 1 atm partial pressure of Ha, all of which may be unrealistic. If the ferredoxin and C3 were predominantly in the reduced state, and if the partial pressure of Ha was low, then the ferredoxin and C3 potentials would be shifted down, and the hydrogen potential would be raised. The issue is not whether this electron transport chain works it does. The problem is only to reconcile this with the standard reduction potentials by an appropriate adjustment of concentrations. 

One of the most troublesome aspects of water-based slip development is the high dielectric constant of the "universal solvent," which, after a few steps of logic, which we ll exclude to give you a puzzle to ponder, leads to the point that water-based slip formulations tend to be aggressively powder dependent. Where a PVB slip might be useful for alumina, zirconia, titania, ferrite, and nickel metal, a water-based slip will tend to work only for one certain powder chemistry and fail miserably for other similar powders. 

Applying ICAM as a predictive tool allows the organization to identify and retain information on causal factors, so the organization remembers that the accident occurred, what caused it, and why procedures were changed. R. Wood (1997) states Beyond question, the most difficult and troublesome aspect of aircraft accident investigation is the determination of cause. ... 

One of the most troublesome aspects of gas-solid flow design is devising a proper feeder. Blow tanks are simple devices for penumatic conveying of solids. Basically, the tank is filled with the solid and emptied through a pipeline by the expanding compressed gas admitted to the tank. These units can operate under a wide range of... 

---