Sacrificial method

Batch methods can be separated further into two general types, experiments that sacrifice the entire volume of an individual reactor and experiments that remove sample aliquots from a single larger reactor. Both types of experiment require that the material of interest be placed in a vessel and stirred continuously to ensure that the effect of transport processes is minimized. In the sacrificial method, at certain time during the course of an experiment, a small-volume reactor is sacrificed and used for analysis. This method eliminates the concentrating effect of removing sample aliquots however, it requires a matrix of experimental vessels to define the system. The aliquot method does restrict the number of samples able to be withdrawn from the system however, it is less labor intensive in terms of the experimental matrix and allows for easier alteration of system conditions. 

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. 

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). 

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. 

There are two principal methods of applying cathodic protection, viz. the impressed current technique and the use of sacrificial anodes. The former includes the structure as part of a driven electrochemical cell and the latter includes the structure as part of a spontaneous galvanic cell. 

The forms of corrosion which can be controlled by cathodic protection include all forms of general corrosion, pitting corrosion, graphitic corrosion, crevice corrosion, stress-corrosion cracking, corrosion fatigue, cavitation corrosion, bacterial corrosion, etc. This section deals exclusively with the practical application of cathodic protection principally using the impressed-current method. The application of cathodic protection using sacrificial anodes is dealt with in Section 10.2. 

Sprayed zinc coalings Details of the method and the nature of the coatings are given in Section 12.4. In this method there is no alloy formation and the bond is primarily mechanical. Although porous, the coating is protective partly due to its sacrificial action and partly due to the zinc corrosion products which soon block up the pores, stifling further attack. 

Powder coating is a solventless coating system that is not dependent upon a sacrificial medium such as a solvent, but is based on the performance constituents of solid TP or TS plastics. It can be a homogeneous blend of the plastic with fillers and additives in the form of a dry, fine-particle-size compound similar to flour. The three basic methods are the fluidized bed, electrostatic spray, and electrostatic fluidized bed processes (9). 

Additional means of reducing corrosion were the use of prepared steel laths, which were introduced into the FW system and would preferentially rust, leaving boiler tubes unscathed. Sacrificial zinc sheet anodes also were employed, but neither method ensured complete protection of the overall boiler system, and uniform general corrosion was often replaced by insidious localized corrosion. 

There are a variety of routes currently utilized to fabricate a wide range of hollow capsules of various compositions. Among the more traditional methods are nozzle reactor processes, emnlsion/phase-separation procednres (often combined with sol-gel processing), and sacrificial core techniques [78], Self-assembly is an elegant and attractive approach for the preparation of hollow capsules. Vesicles [79,80], dendrimers [81,82], and block hollow copolymer spheres [83,84] are all examples of self-assembled hollow containers that are promising for the encapsnlation of various materials. 

Another method to synthesize hollow nanocapsules involves the use of nanoparticle templates as the core, growing a shell around them, then subsequently removing the core by dissolution [30-32]. Although this approach is reminiscent of the sacrificial core method, the nanoparticles are first trapped and aligned in membrane pores by vacuum filtration rather than coated while in aqueous solution. The nanoparticles are employed as templates for polymer nucleation and growth Polymerization of a conducting polymer around the nanoparticles results in polymer-coated particles and, following dissolution of the core particles, hollow polymer nanocapsules are obtained. 

Reduction of two different precious metal ions by refluxing in ethanol/water in the presence of PVP gave a colloidal dispersion of core/shell structured bimetallic nanoparticles. In the case of Pd and Au ions, e.g., the colloidal dispersions of bimetallic nanoparticles with a Au core/Pd shell structure are produced. In contrast, it is difficult to prepare bimetallic nanoparticles with the inverted core/shell (in this case, Pd-core/Au-shell) structure. The sacrificial hydrogen strategy was used to construct the inverted core/shell structure, where the colloidal dispersions of Pd-cores are treated with hydrogen and then the solution of the second element, Au ions, is slowly added to the dispersions. This novel method, developed by us, gave the inverted core/shell structured bimetallic nanoparticles. The Pd-core/Au-shell structure was confirmed by FT-IR spectra of adsorbed CO [144]. 

In the refining of the Group V metals (which are more accurately represented as metal-carbon-oxygen alloys), carbon deoxidation is not the only method by which oxygen is removed, because sacrificial deoxidation also occurs simultaneously. The relative extents to which each of these two deoxidation modes contributes to the overall removal of oxygen can be assessed by calculating the ratio of the vapor pressures of carbon monoxide and the metal monoxide over the M-C-0 alloy. The value of this ratio for vanadium at 2000 K is given by the expression... 

As mentioned in Section 5.2.2, the LbL method generally involves the addition of alternately charged layers, often on to a sacrificial solid that has a charged surface (Figure 5.4). 

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