Sacrificial

For practical applicability, several aspects have to be considered such as tire anode material (sacrificial (e.g. zinc) or inert (e.g. Pt/Ti or graphite)), tlie conductivity of tlie medium and tlie current distribution. Catliodic protection is typically used for buried constmctions (e.g. pipelines), off-shore stmctures or ship hulls. 

The coating has an that is negative to the material to be protected and the layer serves as a sacrificial anode. 

Aromatic perfluoroaLkylation can be effected by fluorinated aUphatics via different techniques. One category features copper-assisted coupling of aryl hahdes with perfluoroalkyl iodides (eg, CF I) (111,112) or difluoromethane derivatives such as CF2Br2 (Burton s reagent) (113,114), as well as electrochemical trifluoromethylation using CF Br with a sacrificial copper anode (115). Extmsion of spacer groups attached to the fluoroalkyl moiety, eg,... 

Electroreductive coupling of ben2otrifluorides with sacrificial aluminum or magnesium anodes in the presence of acetone, carbon dioxide, or /V, /V-dimethylformamide provides a novel route to ArCF2-derivatives (310). 

Because of Hquid helium s uniquely low temperature and small heat of vaporization, containers for its storage and transportation must be exceedingly weU insulated. Some containers are insulated with only a fairly thick layer of very efficient insulation, but containers with the least heat leak use an inexpensive sacrificial cryogenic Hquid, usually Hquid nitrogen, to shield thermally the Hquid helium contents. 

Sacrificial adsorption agents such as lignosulfonates (148—151) can be used to reduce the adsorption of more expensive polymers and surfactants. Other chemicals tested include poly(vinyl alcohol) (152), sulfonated poly(vinyl alcohol) (153), sulfonatedpoly(vinylpyrrohdinone) (153), low molecular weight polyacrylates (154), and sodium carbonate (155). 

Lignosulfonate has been reported to increase foam stabihty and function as a sacrificial adsorption agent (175). Addition of sodium carbonate or sodium bicarbonate to the surfactant solution reduces surfactant adsorption by increasing the aqueous-phase pH (176). 

H2 or O2 from water in the presence of a sacrificial reductant or oxidant employ a mthenium complex, typically [Ru(bipy)2], as the photon absorber (96,97). A series of mixed binuclear mthenium complexes having a variety of bridging ligands have been the subject of numerous studies into the nature of bimolecular electron-transfer reactions and have been extensively reviewed (99—102). The first example of this system, reported in 1969 (103), is the Creutz-Taube complex [35599-57-6] [Ru2(pyz)(NH3. 

AJ—Zn. Aluminum-rich binary ahoys (Fig. 18) are not age hardenable to any commercial significance, and 2inc [7440-66-6] Zn, additions do not significantly increase the abhity of aluminum to strain harden. Al—Zn ahoys find commercial use as sacrificial claddings on high strength Al—Cu—Mg—Zn aircraft ahoy sheet. The eutectoid composition near 78% Zn has found use as a superplastic sheet ahoy. 

Transparent fused silica can be formed at a temperature of 1200°C and a pressure of 13.8 MPa (2000 psi) from silica powder consisting of 15 nm ultimate particles (92) or by electric arc fusion of pure silica sand having low iron and alkali metal contents. The cooled product is ground to the desired particle size. Fused sihca is primarily manufactured by C-E Minerals, Minco, and Precision Electro Minerals in the United States by Chuo Denko, Denki Kagaku Kogyo, NKK, Showa Denko, and Toshiba Ceramics in Japan. Based on 1988 data and projected growth, an estimated 135,000 metric tons of fused siUca were used in 1994 as a sacrificial component or investment casting in the manufacture of metals and as a component in refractory materials (62). 

Galvanic corrosion can be controlled by the use of sacrificial anodes. This is a common method of controlling corrosion in heat exchangers with Admiralty tube bundles and carbon steel tube sheets and channel heads. The anodes are bolted direcdy to the steel and protect a limited area around the anode. Proper placement of sacrificial anodes is a precise science. 

The most significant chemical property of zinc is its high reduction potential. Zinc, which is above iron in the electromotive series, displaces iron ions from solution and prevents dissolution of the iron. For this reason, zinc is used extensively in coating steel, eg, by galvanizing and in zinc dust paints, and as a sacrificial anode in protecting pipelines, ship hulls, etc. 

Other methods of preparing tertiary bismuthines have been used only to a limited extent. These methods iaclude the electrolysis of organometaUic compounds at a sacrificial bismuth anode (54), the reaction between a sodium—bismuth or potassium—bismuth alloy and an alkyl or aryl haUde (55), the thermal elimination of sulfur dioxide from tris(arenesulfiaato)bismuthines (56), and the iateraction of ketene and a ttis(dialkylainino)bismuthine (57). 

Aluminum alloy (and in particular alclad aluminum) tubing is sometimes used in water service. The alclad alloy has a sacrificial aluminum-alloy layer metallurgically bonded to a core alloy. 

Continuous Cake Filters Continuous cake filters are apphcable when cake formation is fairly rapid, as in situations in which slurry flow is greater than about 5 L/min (1 to 2 gal/min), shiny concentration is greater than 1 percent, and particles are greater than 0.5 [Lm in diameter. Liquid viscosity below 0.1 Pa s (100 cP) is usually required for maintaining rapid liquid flow through the cake. Some designs of continuous filters can compromise some of these guidelines by sacrificial use of filter aid when the cake is not the desired product. 

Two methods of providing cathodic protection for minimizing corrosion of metals are in use today. These are the sacrificial-anode method and the impressed-emf method. Both depend upon making the metal to be protected the cathode in the electrolyte involved. 

Examples of the sacrificial-anode method include the use of zinc, magnesium, or aluminum as anodes in electrical contact with the metal to be protected. These may be anodes buried in the ground for protection of underground pipe lines or attachments to the surfaces of equipment such as condenser water boxes or on ship hulls. The current required is generated in this method by corrosion of the sacrificial-anode material. In the case of the impressed emf, the direct current is provided by external sources and is passed through the system by use of essentially nonsacrificial anodes such as carbon, noncor-rodible alloys, or platinum buried in the ground or suspended in the electrolyte in the case of aqueous systems. 

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