Cathode deposition

The purification of the galHum salt solutions is carried out by solvent extraction and/or by ion exchange. The most effective extractants are dialkyl-phosphates in sulfate medium and ethers, ketones (qv), alcohols, and trialkyl-phosphates in chloride medium. Electrorefining, ie, anodic dissolution and simultaneous cathodic deposition, is also used to purify metallic galHum. 

Manganese metal made by this process is 99.9% pure. It is in the form of irregular flakes (broken cathode deposits) about 3-mm thick, and because of its brittleness, has Httle use alone. Most of the electrolytic manganese that is used in the aluminum industry is ground to a fine size and compacted with granulated aluminum to form briquettes that typically contain 75% Mn and 25% Al. 

Electrorefining. Electrolytic refining is a purification process in which an impure metal anode is dissolved electrochemicaHy in a solution of a salt of the metal to be refined, and then recovered as a pure cathodic deposit. Electrorefining is a more efficient purification process than other chemical methods because of its selectivity. In particular, for metals such as copper, silver, gold, and lead, which exhibit Htfle irreversibHity, the operating electrode potential is close to the reversible potential, and a sharp separation can be accompHshed, both at the anode where more noble metals do not dissolve and at the cathode where more active metals do not deposit. 

An electrolytic process for purifying cmde vanadium has been developed at the U.S. Bureau of Mines (16). It involves the cathodic deposition of vanadium from an electrolyte consisting of a solution of VCI2 in a fused KCl—LiCl eutectic. The vanadium content of the mixture is 2—5 wt % and the operating temperature of the cell is 650—675°C. Metal crystals or flakes of up to 99.995% purity have been obtained by this method. 

Fire Refining. The impurities in bhster copper obtained from converters must be reduced before the bUster can be fabricated or cast into anodes to be electrolyticaHy refined. High sulfur and oxygen levels result in excessive gas evolution during casting and uneven anode surfaces. Such anodes result in low current efficiencies and uneven cathode deposits with excessive impurities. Fite refining is essential whether the copper is to be marketed directly or electrorefined. 

The series system was used in the past as an alternative to the multiple system. In this system only anodes were charged and a potential was maintained between the ends of each cell so that copper dissolved from one anode was plated on the adjacent anode. After a sufficient period of time, all the original anode copper was replaced by a cathodic deposit and the impurities were either in the form of anode slime or in solution. The series system demanded highly uniform anodes, a requirement that was difficult to meet with horizontal equipment. 

Composition, temperature, and flow rate of the electrolyte are of great importance to the quafity of the cathode deposit, and changes in any one of these parameters can have a serious effect. Storage and circulation of the electrolyte are also significant. The total volume of electrolyte in a modem tank house is typically 6000 m for a copper production level of ca 500 t/d. 

The use of an extractant depends on loading capacity, extraction rate, pH range, and the cost of the reagent and the diluent. Loss of the extractant must be minimised because of its high cost. Organic losses to the aqueous phase are also undesirable because of the deleterious effect on cathode deposits. Advances in SX—EW processes are described in Reference 38. 

One of us (RES) suggested over two years ago[6] that the resolution to this question lies in the electric field inherent to the arc plasma. As argued then, neither thermal nor concentration gradients are close to the magnitudes required to influence tip annealing, and trace impurities such as hydrogen, which might keep the tip open, should have almost no chemisorption residence time at 3000°C. The fact that w ell-formed nanotubes are found only in the cathode deposit, where... 

Statistics from 60 tubes from 40 tubes from over 100 tubes from 70 tubes from over 300 tubes Nanotubes grew radially out of YC, crystals, 15-100 nm long Nanotubes found in the cathode deposit, 3-40 nm long "Nanotubes formed by pyrolysis on graphite substrate. 

Fig. 7. First-order Raman spectra of (a) graphite, (b) inner core material containing nested nanotubes, (e) outer shell of carbonaceous cathode deposit (after ref. [24]).

The spacings between the layers (rfooz) measured by selected area electron diffraction were in a range of 0.34 to 0.35 nm[3]. X-ray diffraction (XRD) of the cathode deposit, including nanoparticles and nano-... 

For Sm, Eu, and Yb, on the other hand, nanocapsules containing carbides were not found in the cathode deposit by either TEM or XRD. To see where these elements went, the soot particles deposited on the walls of the reaction chamber was investigated for Sm. XRD of the soot produced from Sm203/C composite anodes showed the presence of oxide (Sm203) and a small amount of carbide (SmC2). TEM, on the other hand, revealed that Sm oxides were naked, while Sm carbides were embedded in flocks of amorphous carbon[12J. The size of these compound particles was in a range from 10 to 50 nm. However, no polyhedral nanocapsules encaging Sm carbides were found so far. 

Magnetic properties of iron nanocrystals nested in carbon cages, which grew on the cathode deposit, have been studied by Fliura el al.[29]. Magnetization (M-H) curves showed that the coercive force. He, of... 

MWCNT grows only inside the cathode deposit and does not exist in other places in the reactor. Quantity of MWCNT obtained depends on the pressure of He atmosphere in the reactor, which is the most important parameter. The highest quantity of MWCNT is obtained when the pressure of He is ca. 500 Torr. When this value becomes below 100 Torr, almost no MWCNT grow. This contrasts to that the highest quantity of fullerene is obtained when the pressure becomes 100 Torr or less. 

Another important parameter is the electric current for discharge. If the current density is too high, the quantity of the hard shell increases and that of the MWCNT decreases. To keep the arc discharge stable and the electrode cool are effective to increase in the product quantity of MWCNT. A considerable quantity of graphite is produced in the cathode deposit even under the most suitable condition to the synthesis of MWCNT. 

Fig. 1. The rotating-cathode DC arc method [6a]. The cathode deposit is immediately taken out of the discharge by rotation and cropped within one turn. This method offers high stability and reliability of the handling and makes the continuous mass production possible.

Soot" and "Extended deposit" protruding from the usual cathodic deposit, and "Weblike deposit."... 

The CNT cavity is not directly accessible for experiments for CNTs obtained from the cathode deposit because, their tips are almost always closed by multishell hemispherical or polyhedral domes. The first step of any capillaryfilling procedure consists of an opening process, that will be discussed in detail in the following section. 

Other oxides of phosphorus are less well characterized though the suboxide PO and the peroxide P2O6 seem to be definite compounds. PO was obtained as a brown cathodic deposit when a saturated solution of Et3NHCl in anhydrous POCI3 was electrolysed between Pt electrodes at 0°. Alternatively it can be made by the slow reaction of POBrs with Mg in Et20 under reflux ... 

Kathoden-dichte, /. cathode density, -fiache, /. cathode surface, -licht, n. cathode glow, -niederschlag, m. cathode deposit, -raum, m. cathode space, space aroimd the cathode, -rdhre, /. cathode-ray tube, -strahl, m. cathode ray. -strahlenbiindel. n. cathode beam, -strahlrbhre, /. cathode-ray tube, -strahlimg. /. cathode radiation, -strom, m. cathode current, -zerstaubimg, /. cathode sputtering. 

Lucey concludes from his electrochemical studies that dezincification involves anodic dissolution of both copper and zinc followed by the cathodic deposition of copper, and on this basis he has explained why arsenic is capable of inhibiting dezincification of a-brass but not of a 3-brass. 

Porosity As is the case with all cathodic deposits, the corrosion resistance of a copper deposit is reduced in the presence of continuous porosity. Experience has shown that porosity is least when attention is paid to adequate cleaning, and the solution is kept free from solid or dissolved impurities (see Section 12.1). Porosity of copper deposits is also related to polarisation . 

Pandya et al. have used extended X-ray ascription fine structure (EXAFS) to study both cathodically deposited -Ni(OH)2 and chemically prepared / -Ni(OH)2 [44], Measurements were done at both 77 and 297 K. The results for / -Ni(OH)2 are in agreement with the neutron diffraction data [22]. In the case of -Ni(OH)2 they found a contraction in the first Ni-Ni bond distance in the basal plane. The value was 3.13A for / -Ni(OH)2 and 3.08A for a-Ni(OH)2. The fact that a similar significant contraction of 0.05A was seen at both 77 and 297K when using two reference compounds (NiO and / -Ni(OH)2) led them to conclude that the contraction was a real effect and not an artifact due to structural disorder. They speculate that the contraction may be due to hydrogen bonding of OH groups in the brucite planes with intercalated water molecules. These ex-situ results on a - Ni(OH)2 were compared with in-situ results in I mol L"1 KOH. In the ex-situ experiments the a - Ni(OH)2 was prepared electrochemi-cally, washed with water and dried in vac-... 

Matsuda and co-workers [39-41] proposed the addition of some inorganic ions, such as Mg2+, Zn2+, In3+, Ga3+, Al3+,and Sn2+, to PC-based electrolytes in order to improve cycle life. They observed the formation of thin layers of Li/M alloys on the electrode surface during the cathodic deposition of lithium on charge-discharge cycling. The resulting films suppress the dendritic deposition of lithium [40, 41]. The Li/Al layer exhibited low and stable resistance in the electrolyte, but the... 

About 20 amalgam-forming metals, including Pb, Sn, Cu, Zn, Cd, Bi, Sb, Tl, Ga, In and Mn, are easily measurable by stripping strategies (ASV and PSA) based on cathodic deposition onto mercury electrodes. Additional metals, such as Se, Hg, Ag, Te and As are measurable at bare solid electrodes such as carbon or gold. 

The isomerization of 1-butene to cis- and trans- 2-butene onPd/C/Nafion and Pd-Ru/Nafion electrodes is one of the most remarkable and astonishing electrochemical promotion studies which has appeared in the literature.39,40 Smotkin and coworkers39,40 were investigating the electrocatalytic reduction of 1-butene to butane on high surface area Pd/C and Pd-Ru cathodes deposited on Nafion 117 when, to their great surprise, they observed at slightly negative overpotentials (Fig. 9.31) the massive production of 1-butene isomerization, rather than reduction, products, i.e. cis- and trans-2-butenes. This is extremely important as it shows that electrochemical promotion can be used also to enhance nonredox catalytic reactions such as isomerization processes. 

The electrochemical preparation of metal chalcogenide compounds has been demonstrated by numerous research groups and reviewed in a number of publications [ 1-3]. For the most part, the methods that have been used comprise (a) cathodic co-reduction of the metal ion and a chalcogen oxoanion in aqueous solution onto an inert substrate (b) cathodic deposition from a solvent containing metal ions and the chalcogen in elemental form (the chalcogens are not soluble in water under normal conditions, so these reactions are carried out in non-aqueous solvents) (c) anodic oxidation of the parent metal in a chalconide-containing aqueous electrolyte. 

Skyllas-Kazacos [14] proposed a different method of cathodic deposition with low-oxidation chalcogen precursors, involving cyanide aqueous solutions of elemental Se and Te, where the chalcogen was presumed to be present as SeCN or TeCN ions, respectively. Deposition results were only reported for CdSe and CdTe, indicating a nearly amorphous (nanocrystalline) nature of the films, which though did not contain free Se or Te. 

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