Sacrificial Process

Sacrificial process is an extremely important concept for creating movable structures on a substrate. Structural materials must be anchored onto the substrate but a gap must be left between the structural material and the substrate to allow motion of the structure. Since we cannot deposit a structural material suspended in air, the ultimate gap must be occupied initially by a material that will be removed eventually. It is known as a sacrificial material and its removal is called release. 

Sacrificial process to create a polycrystalKne silicon cantilever beam, (a) SiN layer is deposited onto Si substrate as insulating layer, (b) SiOj layer is deposited as sacrificial layer. 

Note that the Si02 layer underneath serves as a place holder for the ultimate air gap between the polycrystalline silicon cantilever and the substrate. Now we can release the cantilever by etching away the sacrificial Si02. This is done in a wet etching step utilizing hydrofluoric acid (HF). 

---

Cooperation between aromatic amines and hindered phenolic AO or phenolic sulfides was used for explanation of homosynergism [3,49,250], Due to the higher rate constants of ROO with amines in comparison with that of phenols, amines react in the sacrificial process faster than phenols. The latter serve as hydrogen donors for the aminyl radical and a part of the parent amine is cyclically regenerated. The rate constant of the reaction (Eq. 48, ArOH = phenolic AO) is of the order 107 dm3 mol-1 s-1 and is equal or higher than that for Eq. (1) [50]. 

These compounds are commonly used to stabilize thermoplastic polymers during processing in the melt at temperatures up to 300 °C. Their contribution to the long-term stabilization of polymers at ambient temperatures is small but not negligible. Phosphite stabilizers destroy hydroperoxides stoichiometrically in a sacrificial process, as shown in Scheme 9.19. 

In addition to the three basic microfabrication steps discussed above, other fabrication techniques are quite useful. We will briefly discuss a few of them, namely lift-off, annealing, liquid phase photopolymerization, micromolding, soft lithography, electroplating, sacrificial processes, bonding, surface modification, laser-assisted processes, planarization, and fabrication on flexible substrates and curved surfaces. Some of these techniques do not necessarily belong to the traditional repertoire of microfabrication of ICs. However, they have proved very useful for the creation of other types of microdevices and systems such as MEMS, microfluidics, and labs on chips. 

Sacrificial anode systems operate without external power source. The anodes are reactive metals such as magnesium and zinc or aluminum alloys. The energy for the process is derived from the anode material. Careful design is required to match the output and lifetime of the anodes with the polarization and life-expectancy requirements of the plant. Sacrificial anode CP is used for offshore platforms, sub-sea pipelines and the inside of ballast tanks on tanker ships. 

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). 

Foods such as meat, fish, and some vegetables contain sulfur-bearing amino acids that form volatile sulfur compounds during processing and storage. When these compounds react with iron, a black precipitate forms on the container and in most instances darkens the food. A small piece of aluminum welded to the tinplate can has been used to prevent container corrosion and sulfide staining in commercially canned hams. In this case, the aluminum acts as a sacrificial anode and stops the reaction with tin and iron that otherwise could occur at the small exposed tinplate areas (14). 

Titanium is used as a sacrificial barrier, that is, it is gradually consumed during the heating process. It is deposited by CVD or sputtering (see Ch. 6). 

The originality of our approach lies in the elaboration of a sacrificial layer and of a sfrucfural layer made wifh low-femperafure processes, suifable for infegrafion of fhe optical archifecfure on fop of fhe driving circuif realized in fhe subsfrafe (Zamkofsian ef ah, 2002b). 

The critical operation is the etching of the sacrificial layer. With a proper wet etching process, the remaining structural layer shows a high quality surface (Fig. 8). The 10 pm thick sacrificial layer has been etched and the layer stays with a perfect plane shape. Stiffness of the structural layer is also visible in Fig. 8b where the substrate have been cleaved near a structure. Attachment points are 500 pm away and there is no bending of the structure. 

Though short fiber-reinforced mbber composites find application in hose, belt, tires, and automotives [57,98,133,164] recent attention has been focused on the suitability of such composites in high-performance applications. One of the most important recent applications of short fiber-mbber composite is as thermal insulators where the material will protect the metallic casing by undergoing a process called ablation, which is described in a broad sense as the sacrificial removal of material to protect stmcrnres subjected to high rates of heat transfer [190]. Fiber-reinforced polymer composites are potential ablative materials because of their high specific heat, low thermal conductivity, and ability of the fiber to retain the char formed during ablation [191-194]. 

In the future, further studies should be addressed to improve the chemose-lectivity and diastereoselectivity of the reductive coupling process, especially searching for novel reagents and milder experimental conditions. As a matter of fact, a few novel reductive couphng procedures which showed improved efficiency and/or stereoselectivity have not been further apphed to optically active imines. For example, a new electrochemical procedure which makes use of the spatially addressable electrolysis platform with a stainless steel cathode and a sacrificial aluminum anode has been developed for imines derived from aromatic aldehydes, and the use of the N-benzhydryl substituent allowed 1,2-diamines to be obtained with good yields and dl-to-meso ratios... 

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. 

Various strategies are employed to prevent corrosion. The use of paint as a protective coating is described in our chapter introduction. A metal surface can also be protected by coating it with a thin film of a second metal. When the second metal is easier to oxidize than the first, the process is galvanization. Objects made of iron, including automobile bodies and steel girders, are dipped in molten zinc to provide sacrificial coatings. If a scratch penetrates the zinc film, the iron is still protected because zinc oxidizes preferentially ... 

Using electrons for the electrolytic reduction of metal salts, Reetz and coworkers have introduced a further variation to the tetraalkylammoniumhalide-stabilization mode [192-198]. The overall electrochemical process can be divided into the following steps (i) oxidative dissolution of the sacrificial Metbuik anode, (ii) migration of Met ions to the cathode, (iii) reductive formation of... 

---