Sacrificial aluminum electrodes

The use of sacrificial aluminum electrodes is also effective for the eleetrore-ductive synthesis of disilanes and polysilanes from monochlorosilanes and dichlorosilanes, respectively as reported by Nonaka et al. and Dunogues et al. independently [88],... 

Cathodic reduction of (chloromethyl)dimethylchlorosilane using an aluminum anode provided polycarbosilanes besides a large amount of di- and trisilacyclic compounds (equation 67)97. On the other hand, the electrolysis in the presence of Me2SiCl2 gave bis(dimethylchlorosilyl)methane, a useful polycarbosilane precursor (equation 68)97. Similarly, polycarbosilanes were prepared from dichlorocarbosilanes using sacrificial aluminum electrodes in DME (equation 69)91. 

The use of reactive metal electrodes are also effective for the silylation of various organic halides and simple arenes [75]. For instance, Dunogues et al. reported that electrolysis of aryl chlorides in the presence of excess Me3SiCl in a one-compartment cell equipped with a sacrificial aluminum anode in 80 20 THF/HMPA gave the corresponding aryltrimethylsilanes (Scheme 36). When... 

In a bipolar arrangement, the sacrificial electrodes are placed between the two parallel electrodes without any electrical connection. The two monopolar electrodes are connected to the electric power source with no interconnections between the sacrificial electrodes. This cell arrangement provides a simple setup, which facilitates easy maintenance. When an electric current is passed through the two electrodes, the neutral sides of the conductive plate will be transformed to charged sides, which have opposite charge compared with the parallel side beside it. The sacrificial electrodes are known as bipolar electrodes. It has been reported that EC cell with monopolar electrodes in series connection was more effective where aluminum electrodes were used as sacrificial and iron was used as anode and cathode. And, electrocoagulation with Fe/Al (anode/cathode) was more effective for the treatment process than Fe/Fe electrode pair (Modirshahla et al. 2007). 

A number of other publications deal with the electrochemical behavior of a, oj-dibromoalkanes at mercury electrodes polarographic studies [85,86] electrolyses of 1,3-dibromopropane, 1,4-dibromobutane, and 1,5-dibromopentane [87,88] reduction of 1,10-dibromo- and 1,10-diiododecane [89] and electro syntheses of phenylcyclopropane and cyclopropanol [90]. In the presence of an arylalkene, reduction of 1,3-dibromopropane or 1,4-dibromobutane at nickel in DMF containing TBABr and with a sacrificial aluminum anode yields the corresponding cyclopentane or cyclohexane adduct [32] ... 

Electrochemical dissolution of sacrificial anodes, for example, iron, aluminum, or magnesium, has been proposed for phosphate removal from urine. Ikematsu et al. [15] used an electrochemical reactor craisisting of two DSA and one iron electrode for combined nitrogen oxidation and phosphate precipitatirai. First, urea was oxidized at the DSA, then the current direction was changed, and phosphate was precipitated by dissolving the iron electrode. Zheng et al. [29, 30] used synthetic and real fresh urine for their experiments with iron and aluminum electrodes. With both types of electrodes, complete phosphate removal was achieved. At 40 mA cm and a gap width of 5 mm, 1.3 mol Fe. mol had to be dosed to remove 98 % of the phosphate (calculated by assuming a current efficiency... 

A 5.5 (xm photoresist layer was patterned as the sacrificial layer, followed by the deposition of a second 4.5 p,m parylene layer. The parylene/photoresist/ parylene sandwich structure formed the electrospray nozzle and channel when the photoresist was subsequently dissolved. A 1500 A sputtered aluminum layer was used as a mask for parylene etching to define the shape of the nozzle. Aluminum was removed by a wet etching process. After SU-8 developing, wafers were left inside the SU-8 developer for 2 days to release the photoresist. A serpentine channel (250 pan x 500 pm x 15 mm) extending from the junction of pump channels to the edge of the chip was patterned in the SU-8 layer. Platinum/titanium lines spaced 200 pm apart were patterned under the channel after the electrode deposition step. 

Sacrificial anode — is a piece of metal used as an anode in electrochemical processes where it is intended to be dissolved during the process. In -+ corrosion protection it is a piece of a non-noble metal or metal alloy (e.g., magnesium, aluminum, zinc) attached to the metal to be protected. Because of their relative -+ electrode potentials the latter is established as the -+ cathode und thus immune to corrosion. In -+ electroplating the metal used as anode may serve as a source for replenishing the electrolyte which is consumed by cathodic deposition. The sodium-lead alloy anode used in the electrochemical production of tetraethyl lead may also be considered as a sacrificial anode. 

The General Electric SPE (17) consists of two porous particulate electrodes which are bondecTcohesively with polytetrafluoro-ethylene dispersion particles and connected electrically to the outside of the cell hardware by means of metallic current collectors which are pressed against the SPE by mechanical methods. Such an SPE can be prepared via perfluoroionomer solution techniques. One method is to apply a paste consisting of the electrolyte powder and the perfluoroionomer solution to the membrane and evaporate the solvent. Alternately, the paste can be applied to a sacrificial substrate such as aluminum foil, dried, and subsequently pressed into the membrane as a decal. 

Sacrificial Anodes Incontrastto the impressed current technique, the use of sacrificial anodes does not depend on the creation of driven electrochemical cell. Rather, a galvanic cell is formed between the structure and the sacrificial anode in which electrons pass spontaneously from the latter to the former (Fig. 9). Thus, the source of the electrons (the sacrificial anode) must have a more negative electrode potential than the structure. It was for this reason that Humphrey Davy chose zinc or iron to protect copper, and it also explains why magnesium, aluminum and zinc alloys are used to protect steel today. 

Galvanized steel is a common example of galvanic coupling where steel (Fe), with a standard electrode potential of —0.440 V vs. SHE, is cathodicaUy protected by zinc, which has a more active standard electrode potential of —0.763 V. Obviously, zinc is not a corrosion-resistant metal and cannot be classified as a barrier coating. It protects steel from corrosion through its sacrificial properties. Because zinc is less noble than iron in terms of the standard electrode potentials, it acts as an anode. The sacrificial anode (zinc) is continuously consumed by anodic dissolution reaction and protects the underlying metal (iron in steel) from corrosion. In practice, sacrificial anodes are comprised of zinc, magnesium alloys, or aluminum. 

Cathodic protection (CP) is defined as the reduction or elimination of corrosion by making the metal a cathode by means of impressed current or sacrificial anode (usually magnesimn, aluminum, or zinc) [11]. This method uses cathodic polarization to control electrode kinetics occurring on the metal-electrolyte interface. The principle of cathodic protection can be explained by the Wagner-Traud mixed potential theory [12]. 

Cathodic control protection protects the substrate by coating with a less noble metal, for which the slopes of the cathodic polarization curves are steep. The cathodic overpotential of the surface is increased by the coating therefore, the corrosion potential becomes more negative than that of the substrate. Coating materials used for this purpose are zinc, aluminum, manganese, cadmium, and their alloys. The electrode potential of these metals are more negative than those of iron and steel. When exposed to the environment, these coatings act as sacrificial anodes for the iron and steel substrates. 

When using magnesium as a sacrificial electrode, phosphate can be precipitated as struvite [31]. Stmvite is a preferred product over iron or aluminum phosphates, because it is a better phosphate fertilizer [32]. Without base addition, the process can only be applied to stored urine, because a high pH value is required for struvite formation. 

As can be seen in Table 19.6, aluminum and its alloys become the anode in galvanic cells with most metals and corrode sacrificially to protect them. Only magnesium and zinc are more anodic and corrode to protect aluminum. Neither aluminum nor cadmium corrode sacrificially in a galvanic cell because they have nearly the same electrode potential. 

A If a metal more active than iron, such as magnesium or aluminum, is in electrical contact with iron, the metal rather than the iron wiU he oxidized. This principle underhes the use of sacrificial electrodes to prevent the corrosion of iron. 

It was mentioned earlier that polysUanes could be prepared by electrochemical polymerization of chlorosilanes. In a similar manner, chloromethyldimethylchlorosilane gives reasonable quantities (==40% yield) of relatively low molecular weight polycar-bosilanes using aluminum as a sacrificial electrode and a current density of 2.2 F/mol in a THF/DMF solution with Et4NBF4 as a supporting electrolyte. ... 

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