Metallic collectors

The assembled cell was put between two metal collectors and pressed to the level of operating pressure for purposes of reduction of the contact resistance of assembly parts between power covers of the clamp unit. 

This explosion could have been prevented with a tramp metal collector, for example, a magnetic trap or a screen. An additional safeguard would be the addition of an inerting gas. 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

The mixed-potential model demonstrated the importance of electrode potential in flotation systems. The mixed potential or rest potential of an electrode provides information to determine the identity of the reactions that take place at the mineral surface and the rates of these processes. One approach is to compare the measured rest potential with equilibrium potential for various processes derived from thermodynamic data. Allison et al. (1971,1972) considered that a necessary condition for the electrochemical formation of dithiolate at the mineral surface is that the measmed mixed potential arising from the reduction of oxygen and the oxidation of this collector at the surface must be anodic to the equilibrium potential for the thio ion/dithiolate couple. They correlated the rest potential of a range of sulphide minerals in different thio-collector solutions with the products extracted from the surface as shown in Table 1.2 and 1.3. It can be seen from these Tables that only those minerals exhibiting rest potential in excess of the thio ion/disulphide couple formed dithiolate as a major reaction product. Those minerals which had a rest potential below this value formed the metal collector compoimds, except covellite on which dixanthogen was formed even though the measured rest potential was below the reversible potential. Allison et al. (1972) attributed the behavior to the decomposition of cupric xanthate. 

Table 4.1 shows the measured rest potential of sulphide electrode in thio collector solutions at pH = 6.86 and the equilibrium potential calculated for possible processes. In terms of the mixed potential model, the reaction products should be metal collector salts between four thio collectors and galena and jamesonite and should be disulphide between four thio collectors and pyrite and... 

From the point of view of electrochemistry of flotation, a depressant is, however, defined as a reagent by the addition of which the oxidation of the mineral surface occurs at lower potential than collector oxidation or formation of metal collector salt which may be also decomposed imder the conditions given in the discussions which follow. Under these conditions, the mixed potential model becomes one of mineral oxidation and oxygen reduction, the oxidation of the thio collector or the formation of the metal collector is suppressed, and the mineral will remain... 

The underlying principle of depression by hydroxyl ion is that for each concentration of collector there is a pH below which any given mineral will float and above which it will not float. This is the so-called critical pH which can be determined according to the relative extent of oxidation of the mineral surface and collector or the formation of the metal collector salt. 

A typical configuration of a double-layer supercapacitor involves two metallic collectors which hold in place the carbon powder electrodes, which in turn are separated by an electrolyte, in most of the cases formed by liquid solutions (Fig. 9.28.) A layer of porous, non-conductive material acts as a separator. 

With the introduction in the late 1960s of very high sensitivity instrumentation for the analysis of air and soil gas for Hg, it became possible to determine Hg levels in the field. Air surveys were commonly carried out from vehicles mounted with a precious-metal collector. Mercury within measured volumes of air passing over the collector amalgamated with the precious metal, which was subsequently heated to release the Hg for analysis. A less sensitive alternative method was to pass air directly through a Hg analyser without pre-concentration. 

Ion flotation is a process in which metal ions are removed from dilute, aqueous solutions by interaction with dissolved, surface active organic collectors. The metal-collector complexes or ion pairs adsorb preferentially at solution-air interfaces, and hence can be removed by sparging air through the solution and separating the resulting loam." Precipitate flotation is a related technique in which an insoluble compound that is hydrophobic, or can be rendered so using... 

Fig. 9.14 Scheme for an electron transfer from an excited particle to a metal collector electrode in the absence (a) and in the presence (b) of a redox couple. (After ref. [49])... 

Silver has also been used as the collector [5]. For metals such as Rh, Ir, and Os, good results have been obtained where iron, nickel, copper, tin, and their alloys are used as the collectors [6-8]. Tin [8] and copper [6,7] have also been used, instead of lead, in the separation of gold. If noble metals are separated along with metal collectors, the obtained alloys are dissolved in acid, and the noble metals are separated by chemical methods. Copper sulphide [9] and nickel sulphide [3,10-13] have also been recommended for the separation of noble metals. 

FIGURE 23.14 (a) Bipolar plates and a three-unit cell stack pressed between two metal collector plates,... 

Any electrode involves oxidation and reduction in its operation, but these electrodes have had that superfluous phrase attached to them. An oxidation-reduction electrode has an inert metal collector, usually platinum, immersed in a solution that contains two soluble... 

Because the energy of the secondary electrons is loo low (<50 eV) to excite the scintillator directly, the electrons arc first accelerated. Acceleration is aceon). plished by applying a bias voltage of approximately + 10 keV to a thin film of aluminum covering the scintillator. A positively biased metal collector grid sur-... 

Electrospinning based on the application of a static electric field on a polymer solution or melt through a spinneret appears to be a simple and well-controllable technique able to produce polymeric nanofibers. A typical experimental setup is based on a capillary injection tip, a high-voltage source able to apply electric fields of 100-500 KVm , and a metallic collector, or counter electrode. Electric current in electrospinning experiments is usually in the order of a few milliamperes. ... 

The positive electrode is the metal part of the needle and the negative part of the electrode is the metal collector. About 5 to 180 minutes of operation time was applied for the deposition of fibers on wax paper, aluminum foil, and ITO PET. A horizontal setup was chosen for the electrospinning process. A representative picture of design of electrospinning is illustrated in Fig. 4.5. 

One of the problems with solar-radiation heat collectors has been their inefficient collection of the short-wavelength component of the solar spectrum. When a conventional metallic collector is coated with very fine particles which are absorptive at short wavelengths, the resultant heat generated in the particles can be dissipated by conduction to the collector [1.44]. Both particle optical interactions and microphysics play roles in the design of such particles, and interaction forces are useful for their immobilization. 

This procedure involves the melting of the sample with a variety of powdered reagents to give a metallic (collector) button (e.g., lead) containing the elements of interest or the metalliferous portion, separated from a slag that contains the unwanted portion of the sample, known as the gangue. 

The cell is completed (Figure 6.13) by placing in sequence, on top of the cathodic membrane, the electrolytic film, the lithium foil and a second metal collector (negative terminal) ... 

The literature reports some examples of functional nanofiber mats prepared by simultaneously electrospinning a polymer solution and electrospraying a particle suspension on the same metallic collector. In electrospraying, when the electric force is higher than the surface tension of the liquid, the jets are atomized into fine droplets that are collected as solid particles. In electrospinning, the electric repulsion force cannot overcome the intermolecular forces in the liquid and, hence, the jet extends, bends and eventually reaches the collector, forming a solid fiber. The resulting nonwoven mat is composed of nanoparticles located on the fiber surface and within the pores of the nonwoven structure (Fig. 20). 

The tensile properties can be determined only if the cross section of the specimens is known. In the case of electrospun materials that are deposited on a flat metal collector [106], the area density is not uniform. To avoid this problem, a rotating drum with low velocity is suggested. This slow motion does not affect the orientation of fibers, but the structure has a quasi-constant thickness in the direction of rotation [107], And in this case the linear density in the direction of rotation can also be considered constant. The cross section... 

Figure 19 A Schematics of metallic collectors, (a) Plate, (b) rotating disk, (c) rotating mandrel, (d) two blades, (e) rotating cone.

---