Scale, metal oxide

Y.-X. Li, K.J. Klabunde, Nano-scale metal oxide particles as chemical reagents. Destructive adsorption of a chemical agent simulant, dimethyl methylphosphonate, on heat-treated magnesium oxide. Langmuir 7, 1388-1393 (1991)... 

This chapter presents an overview of structures, properties, synthetic methods and applications in catalysis for highly dispersed metal oxides, with special attention given to recent developments in nano-scale metal oxides. 

Figure 16.3 A flow chart of a typical sol-gel process for preparing nano-scale metal oxide powder.

Sol-gel processes have several advantages over other techniques for the synthesis of nano-scale metal oxides. Because the process begins with a relatively homogeneous mixture, the resulting product is generally a uniform ultra-fine porous powder. Sol-gel processing also has the advantage that it can be scaled up to accommodate industrial-scale production. 

As is hopefully obvious from this chapter and the entire book, the science of metal oxides is vast and requires synergistic contributions from multiple disciplines if the potential of nano-scale metal oxides is to be reached. As the general field of nano-scale materials develops, metal oxides are likely to be at the forefront owing to their stabihty and the intensive studies that have already been reported for their bulk counterparts. 

Lim S, Cho J. PVP-functionalized nanometer scale metal oxide coatings for cathode materials successful application to LiMn204 spinel nanoparticles. Chem Commun 2008 4472. ... 

Fu, Y., Willander, M., Xu, Q.-X. (2006a). Chapter 5 Quantum effects and nanofabrications in scaling metal-oxide-semiconductor devices. In A. A. Balandin 8t K. L. Wang (Eds.), Handbook of semiconductor nanostructures and nanodevices (Vol. 5, pp. 229-256). Los Angeles American Scientific Publishers. 

HCl gas reacts with metal oxides to form chlorides, oxychlorides, and water. Therefore, all the steel equipment should be pickled to remove the oxide scales before it is put in service. Because oxidi2ing agents in the HCl gas such as oxygen or chlorine significantly affect the corrosion rate, it is essential that the operating temperature of the steel equipment be kept below the temperature (316°C) at which ferric chloride is vapori2ed from the metal surface. 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

Only about 10 elements, ie, Cr, Ni, Zn, Sn, In, Ag, Cd, Au, Pb, and Rh, are commercially deposited from aqueous solutions, though alloy deposition such as Cu—Zn (brass), Cu—Sn (bronze), Pb—Sn (solder), Au—Co, Sn—Ni, and Ni—Fe (permalloy) raise this number somewhat. In addition, 10—15 other elements are electrodeposited ia small-scale specialty appHcations. Typically, electrodeposited materials are crystalline, but amorphous metal alloys may also be deposited. One such amorphous alloy is Ni—Cr—P. In some cases, chemical compounds can be electrodeposited at the cathode. For example, black chrome and black molybdenum electrodeposits, both metal oxide particles ia a metallic matrix, are used for decorative purposes and as selective solar thermal absorbers (19). 

Metal Cleaning. Citric acid, partially neutralized to - pH 3.5 with ammonia or triethanolamine, is used to clean metal oxides from the water side of steam boilers and nuclear reactors with a two-step single fill operation (104—122). The resulting surface is clean and passivated. This process has a low corrosion rate and is used for both pre-operational mill scale removal and operational cleaning to restore heat-transfer efficiency. 

Cobalt cannot be classified as an oxidation-resistant metal. Scaling and oxidation rates of unalloyed cobalt in air are 25 times those of nickel. The oxidation resistance of Co has been compared with that of Zr, Ti, Fe, and Be. Cobalt in the hexagonal form (cold-worked specimens) oxidizes more rapidly than in the cubic form (annealed specimens) (3). 

Fig. 1. Technological trends A, components per chip B, minimum feature length , metal oxide semiconductor (MOS) memory A, bipolar memory I MOS logic n, bipolar logic. The designations SSI, MSI, LSI, and VLSI stand for small-, medium-, large-, and very large-scale iategration, respectively.

Mill Scale—an oxide layer on metals produced by metal rolling, hot forming, welding or heat treatment. 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

Figure 8.19 F.llingham diagram for the free energy of formation of metallic oxides. (After F. D. Richardson and J. H. F. Jeffes, J. Iron Steel Inst. 160, 261 (1948).) The oxygen dissociation pressure of a given M - MO system at a given temperature is obtained by joining on the lop left hand to the appropriate point on the M-MO frec-energy line, and extrapolating to the scale on the right hand ordinate for POi (atm).

Other routes include the high-temperature halogenation of metal oxides, sometimes in the presence of carbon, to assist removal of oxygen the source of halogen can be X2, a volatile metal halide CX4 or another organic halide. A few examples of the many reactions that have been used industrially or for laboratory scale preparations are ... 

---