Alloy stabilization

Bonnemann H ef a/1996 Nanoscale colloidal metals and alloys stabilized by solvents and surfactants preparation and use as catalyst precursors J. Organometaii. Chem. 520 143... 

Sueh a behaviour of metastability has been reported in the systems Cu65Pt35 and CuAu3. It has been shown that for inereased annealing time or after meehanieal deformation LRO is obtained, whereas for too short annealing times in homogenised material only the variation of SRO with temperature is deteeted. This may lead to serious misinterpretation of alloy stability if not carefully enough investigated. 

If neither the AC nor the BC component exhibits in any part of its (zero pressure) (x, T) phase diagram the structure a, which though exists in their solid solution, then the latter is of Type III . In this case, the alloy environment stabilizes a structure which is fundamentally new to at least one of its components. Such alloy-stabilized phases with no counterpart in the phase diagram of the constituent components can be formed in bulk equilibrium growth and may be distinguished from the unusual alloy phases that are known to form in extreme non-equilibrium growth methods and in epitaxial forms. 

Wei S-H, Zunger A (1986) Alloy-stabilized semiconducting and magnetic zinc-blende phase of MnTe. Phys Rev Lett 56 2391-2394... 

Figure 3.19 Schematic representation of surface alloy stability tests. White spheres denote adsorbed hydrogen, black spheres denote solute metal atoms, and gray spheres denote host metal atoms. Adapted from [Greeley and Nprskov, 2007] see this reference for more details.

The trend of intermetallic reactivity and alloy stability of V, Nb and Ta with the different elements may be further discussed in terms of the melting points of the compounds as described in the following paragraphs. 

In a similar manner the so-called Zintl salts composed of alkali metal cations and clusters of metals as anions (see Chapter 16) were known in liquid ammonia solution but proved to be impossible to isolate Upon removal of the solvent they reverted to alloys. Stabilization of the cations by complexation with macrocyclic ligands allowed the isolation and determination of the structures of these compounds. 

Soluble Aspirin Paint Pigment Ferrous Glutinate Ferrous Succinate Lithium Hydroxide Tungsten Alloy Stabilized Diazamin... 

If a Brillouin zone is nearly full or nearly empty, the electron concentration may become an important factor in determining alloy stability. This factor forms the basis of the Hume-Rothery rules (8) and is of great importance in intermetallie semiconductors. 

A durable protective coating for high-temperature alloys can be achieved by CVD. Normally, we must consider alloy stabilization in addition to chemical reaction in a controlled environment. The results define the nature of coatings for high-temperature corrosion protection, namely, a thin (1-2 pm) diffused silicon layer that covers the surface and penetrates even the smallest defects, cracks, etc., on the alloy to be protected. This surface modification treatment by CVD can be adapted to other alloys and is technologically simple and relatively inexpensive. 

Alloy stability is always of concern in heterogeneous catalysis, but in electrocatalysis there are new mechanisms for destabilizing alloys, namely electrochemical dissolution or corrosion. Greeley and Norskov developed an intuitive and simple thermodynamic framework for estimating the stability of alloy surfaces in electrochemical environments. " Their scheme is essentially an extension of an atomistic thermodynamic approach that uses chemical potentials to determine stability to one that uses electrochemical potentials to determine stability. They estimate the electrochemical potentials using total energies calculated within DFT and ideal solution behavior of the ions to consider concentration and pH effects. Within this formalism they are able to estimate the dissolution potential of metals in alloys. They further compared the trends in dissolution behavior to trends in segregation behavior and... 

The warm forming behavior of 2014 aluminum alloy stabilized with small Zr additions was studied by employing torsion tests in the temperature and strain rate ranges of 200-300 °C and 10"3-1 s 1 respectively. The alloy ductility was measured as strain to fracture in all the temperature and strain rate investigated by showing a different behavior between 250-300 °C and the lower temperatures. The activation energy of the material was calculated... 

An activity increase was also observed on a partially crystallized Fe-Ni-B alloy (24). Both XPS and UPS revealed reactive surface carbides formed from dissociative CO chemisorption. It was suggested that the proper ensemble size of the partially crystallized alloy stabilizes the reactive surface carbide and establishes an optimum equilibrium between it and the molecular form of CO, which results in the unique, high catalytic activity. 

Tin (Sn)/Pd carbon-supported alloys have shown enhanced activity and stability [67-71]. Although Sn is completely inactive towards formic acid electrooxidation, a decrease in the 3d electronic density has been observed. An atomic ratio of Sn to Pd of 1 1 resulted in the highest overall performance for particles of similar sizes [69, 70]. Eor the aforementioned PdSn/C results, the current density increased 2- to 2.3-fold at 0.4 V vs. RHE. During constant potential holds, the Pd/C has a continued decrease, while the PdSn/C alloys stabilize after 500 s [70]. 

The ferritic alloys have a body centered cubic structure, are mildly hardenable by cold work, have good formability (particularly drawability), and have a range of corrosion resistance. The ferritic alloys are particularly noted for their SCC resistance. A widely used alloy in this group is S43000 (Type 430), which contains 16 % chromium. The S409xx series are 11 % chromium alloys stabilized with titanium. 

Pt-based alloys have been developed for many years to improve the catalytic activity of the oxygen reduction reaction and the methanol oxidation reaction, and reduce Pt loading in the catalyst layers of the PEM fuel cell cathode and anode. Great progress has been made in recent years in terms of alloy activity screening, alloy mechanism discovery, and alloy stability investigation. 

Type 409 stainless is an 11% chromium alloy stabilized with titanium. Its chemical composition will be foimd in Table 7.3. The material can be welded in the field, however, heat treatment improves corrosion resistance. It has a maximum allowable continuous operating temperature of 1300°F (705°C) with an intermittent operating temperature of 1500°F (815°C). It cannot be hardened by heat treatment. 

In 1973, Hastelloy S was developed for gas turbine applications requiring oxidation resistance, good alloy stability, and a low thermal expansion. The chemical composition will be foimd in Table 15.19. Its composition is similar to that of alloys C-4 and C-276, and it has similar corrosion resistance. However, the carbon content may prevent its use in some aqueous media in the as-welded condition. After 10,000 h of aging in the temperature ranges encoimtered in this application, the alloy S welds exhibited 80% of their original ductility. 

Answer by author The Constitution Diagram for Stainless Steel by A, I, Schaeffler provides an estimate of the phases present at room temperature, as determined by the chemical composition equivalents (Ni and Cr). There seems to be no direct corailary between the position of the stainless steel alloy on the Constitution Diagram and the alloys, stability at low temperatures,... 

Uses Water treatment formula to prevent buildup of min. scale and to control corrosion in industrial water circuits mainly used in open cooling water systems incorporated additive controls growth of algae and slime bacteria contains no biocides dispersant and cleaning effects protection against corrosion of steel, copper, and copper alloys stabilization of hardness forming salts even at high water temps. 

Flo 1 1 Exfoliation corrosion of an aluminum alloy stabilizer bracket, (a) Heavy surface corrosion on the stabilizer bracket, (b) Cross section through the bracket showing corroded surface grains and corrosion of grain boundaries of elongated grains... 

Substituting Equations 6.11 and 6.12 into 6.1 and the result into 6.10, a set of alloy stability curves in x and y are obtained for quaternary alloys. These curves are similar to points on the curve in Figure 4.18c at a given temperature and define a region of composition space in which the alloy is unstable and may decompose. In addition to direct calculation from known values, the bond energies in Equation 6.11 may be obtained by fitting observed spinodal decomposition data for pseudobinary alloys in a given quaternary system. 

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