Metals amorphous

Alloys containing both a metal and a metalloid (P, Si, Ge, B) can often be rapidly cooled directly from a melt to form a material with an 

Describe the structures of the following silicate glasses in terms of the Q units present in the network. Describe the types of tetrahedra present and state the percentage of each type present in the structure. 

Calculate the fraction of the appropriate Q units for the following glasses. Indicate which types of units are present. Calculate the number of NBO per tetrahedra for the same glasses. 

Describe the structures of the following borate glasses. How many NBO are present for each glass What percent of the boron ions are in 4-fold coordination  

---

Metallic Glasses. Under highly speciali2ed conditions, the crystalline stmcture of some metals and alloys can be suppressed and they form glasses. These amorphous metals can be made from transition-metal alloys, eg, nickel—2irconium, or transition or noble metals ia combination with metalloid elements, eg, alloys of palladium and siUcon or alloys of iron, phosphoms, and carbon. 

F. E. Tuhotsky, Amorphous Metallic Alloys, Butterworths, London 1983, p. 360. 

E. E. Luborsky, A., Amorphous Metallic Allojs, Butterworths, London, 1983. 

The increased acidity of the larger polymers most likely leads to this reduction in metal ion activity through easier development of active bonding sites in siUcate polymers. Thus, it could be expected that interaction constants between metal ions and polymer sdanol sites vary as a function of time and the sihcate polymer size. The interaction of cations with a siUcate anion leads to a reduction in pH. This produces larger siUcate anions, which in turn increases the complexation of metal ions. Therefore, the metal ion distribution in an amorphous metal sihcate particle is expected to be nonhomogeneous. It is not known whether this occurs, but it is clear that metal ions and siUcates react in a complex process that is comparable to metal ion hydrolysis. The products of the reactions of soluble siUcates with metal salts in concentrated solutions at ambient temperature are considered to be complex mixtures of metal ions and/or metal hydroxides, coagulated coUoidal size siUca species, and siUca gels. 

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). 

Amorphous metals Antiseptics Boron alloys Cosmetics Nuclear applications Nylon... 

Zeolites and Catalytic Cracking. The best-understood metal oxide catalysts are zeoHtes, ie, crystalline aluminosihcates (77—79). The zeoHtes are well understood because they have much more nearly uniform compositions and stmctures than amorphous metal oxides such as siUca and alumina. Here the usage of amorphous refers to results of x-ray diffraction experiments the crystaUites of a metal oxide such as y-Al202 that constitute the microparticles are usually so small that sharp x-ray diffraction patterns are not measured consequendy the soHds are said to be x-ray amorphous or simply amorphous. 

The things that we have been talking about so far - metal crystals, amorphous metals, solid solutions, and solid compounds - are all phases. A phase is a region of material that has uniform physical and chemical properties. Water is a phase - any one drop of water is the same as the next. Ice is another phase - one splinter of ice is the same as any other. But the mixture of ice and water in your glass at dinner is not a single phase because its properties vary as you move from water to ice. Ice + water is a two-phase mixture. 

We now apply the thermodynamic and kinetic theory of Chapters 5-8 to four problems making rain getting fine-grained castings growing crystals for semiconductors and making amorphous metals. 

Fig. 9.11. Ribbons or wires of amorphous metal con be mode by melt spinning. There is on upper limit on the thickness of the ribbon if it is too thick it will not cool quickly enough and the liquid will crystallise.

Why is it easy to produce amorphous polymers and glasses, but difficult to produce amorphous metals ... 

Coutts, T.J. (1974) Electrical Conduction in Thin Metal Films (Elsevier, Amsterdam). DeCristofaro, N. (1998) Amorphous metals in electric-power distribution applications, MRS Bull. 23(5). 50. 

G. Kresse, Proceedings 9th Intern. Conference in Liquid and Amorphous Metals (LAM9), Chicago 1995 (in print). 

P. Haasen and R. I. Jafife, Amorphous Metals and Semiconductors, Pergamon, London (1986). 

A. Aronin, G. Abrosimova, and I. Zver kova, Proc. 9th Inti. Conf. on Liquid and Amorphous Metals, J. Non-Cryst. Solids, in press, 1996. 

Ichinose, I. and Kunitake T. (2002) Wrapping and inclusion of organic molecules with ultrathin, amorphous metal oxide films. Chemical Record, 2, 339-351. 

Diffusion coefficients in amorphous solids such as oxide glasses and glasslike amorphous metals can be measured using any of the methods applicable to crystals. In this way it is possible to obtain the diffusion coefficients of, say, alkah and alkaline earth metals in silicate glasses or the diffusion of metal impurities in amorphous alloys. Unlike diffusion in crystals, diffusion coefficients in amorphous solids tend to alter over time, due to relaxation of the amorphous state at the temperature of the diffusion experiment. 

Catalysis by sol gel doped silica-based materials has become in the last 20 years a prominent tool to synthesize a vast number of useful molecules both in the laboratory and in industrial plants.12 The underlying basic concept of all sol-gel applications is unique one or more host molecules are entrapped by a sol-gel process within the cages of an amorphous metal oxide where they are accessible to diffusible reactants through the inner pore network, which leads to chemical interactions and reactions (Figure 5.3). 

Bonnemann, EL, Brijoux, W., and Joussen, T., (to Studiengesellschaft Kohle mbH) Microcrystalline-to-amorphous metal and/ or alloy powders dissolved without protective colloid in organic solvents, U.S.Pat, 5, 580,492, 1993. 

The precursor alloy is quenched to form small grains readily attacked by the caustic solution [31], Quenching can also enable specific intermetallic phases to be obtained, although this is less common. Yamauchi et al. [32-34] have employed a very fast quench to obtain a supersaturation of promoter species in the alloy. It is even possible to obtain an amorphous metal glass of an alloy, and Deng et al. [35] provide a review of this area, particularly with Ni, Ni-P, Ni-B, Ni-Co, and Ni-Co-B systems. The increased catalytic activity observed with these leached amorphous alloy systems can be attributed to either chemical promotion of the catalyzed reaction or an increased surface area of the leached catalyst, depending on the components present in the original alloy. Promotion with additives is considered in more detail later. 

Metal oxides were also chirally modified and few of them showed a significant or at least useful e.s. Thus, while Al203/alkaloid [80] showed no enantiodifferentiation, Zn, Cu, and Cd tartrate salts were quite selective for a carbene addition (45% e.e.) [81] and for the nucleophilic ring opening of epoxides (up to 85% e.e.) [82], Recently, it was claimed that /(-zeolite, partially enriched in the chiral polymorph A, catalyzed the ring opening of an epoxide with low but significant e.s. (5% e.e.) [83], All these catalysts are notyet practically important but rather demonstrate that amorphous metal oxides can be modified successfully. 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

---