Dense alloying

Conversely, transmission geometry requires that the sample is minimally absorbing. This is usually not a problem if the studied specimen is a molecular substance. However, when the material is a dense alloy or intermetallic compound containing heavy elements, the preparation of a high quality specimen for transmission powder diffraction may be problematic. With flat transmission samples the best approach is to try to arrange no more than a single layer of particles mounted on the film. When cylindrical specimens are employed, the radius of the capillary should be reduced to a practical minimum. Unfortunately, these measures usually reduce the... 

Surfaces can also be coated without involving electricity. Electroless nickel plating, for example, involves pretreating the surface of any material, including nonconductive materials, with a catalyst such as sodium hypophosphite. This treated surface is then immersed in a heated nickel-phosphorous or nickel-boron solution. The metal ions from the solution are reduced to metal in contact with the catalyst and form a dense alloy layer on the treated surface. 

Terneplate is a tin-lead alloy coated sheet steel, and is produced either by hot dipping or electrodeposition. The hot dipping process with a chloride flux is used to produce most temeplates. The coating layer, whose electrode potential is more noble than that of the steel substrate, contains 8-16% Sn. Since the electrode potential of the coating layer is more noble than the steel substrate, it is necessary to build a uniform and dense alloy layer (FeSn2) in order to form a pinhole free deposit. 

Extensive work has been dedicated to the development of protective coatings for SOFC interconnects (see Future Fuel Cells ). Mitigation of Cr evaporation and excessive growth of oxide scale can be achieved with the use of a protective layer and a contact layer deposited on the dense alloy. The protective layer is obtained with the deposition of Co-Mn oxides to form (Mn,Co,Cr)304 spinel layer [4-6]. 

Preferential segregation of certain elements from dense alloy membranes can also result in degradation of the performance of H2 permeation membranes. For example, Pd-Ag films ( 2.4%Ag, 20-26 pm thick) were deposited by sequential electroless plating onto porous tubular stainless steel substrates with AI2O3 oxide layers to modify the substrate pore size and to prevent intermetallic diffusion of the stainless steel components into the Pd-Ag layer (Bosko et al., 2011). Composite membranes annealed at temperatures of 500-600°C were characterized for film structure (XRD), morphology (SEM), bulk and surface component distribution (EDS, XPS), and H2 permeance. Composition measurements within the Pd-Ag layer revealed preferential segregation of the Ag component to the top surface. This result is consistent with the lower surface free energy of Ag. 

The addition of small amounts of alloying materials greatly improves corrosion resistance to atmospheric environments but does not have much effect against liquid corrosives. The alloying elements produce a tight, dense adherent rust film, but in acid or alkaline solutions corrosion is about equivalent to that of carbon steel. However, the greater strength permits thinner walls in process equipment made from low-alloy steel. 

There are no films or protective surface films on active metals, e.g., mild steel in acid or saline solutions. Passive metals are protected by dense, less readily soluble surface films (see Section 2.3.1.2). These include, for example, high-alloy Cr steels and NiCr alloys as well as A1 and Ti in neutral solutions. Selective corrosion of alloys is largely a result of local concentration differences of alloying elements which are important for corrosion resistance e.g., Cr [4],... 

This example of aluminium illustrates the importance of the protective him, and hlms that are hard, dense and adherent will provide better protection than those that are loosely adherent or that are brittle and therefore crack and spall when the metal is subjected to stress. The ability of the metal to reform a protective him is highly important and metals like titanium and tantalum that are readily passivated are more resistant to erosion-corrosion than copper, brass, lead and some of the stainless steels. There is some evidence that the hardness of a metal is a signihcant factor in resistance to erosion-corrosion, but since alloying to increase hardness will also affect the chemical properties of the alloy it is difficult to separate these two factors. Thus althou copper is highly susceptible to impingement attack its resistance increases with increase in zinc content, with a corresponding increase in hardness. However, the increase in resistance to attack is due to the formation of a more protective him rather than to an increase in hardness. 

Besides the measures described in the main part of this paper, significant improvement of the corrosion resistance of a material can be obtained by use of inhibitors. In this case, good results seem to be achieved with rare earths employed in low amounts as alloying metals or as protective dense oxide coatings. The use of coatings often means the research into the best compromise between mechanical properties and corrosion resistance of the material. 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

Formation of single-phase ZnTe on zinc substrates at 640 K by using electrochemical ion exchange and chemical reaction/alloying with Te" species, supplied to the substrate as a vapor from TeCU-containing eutectic LiCl-KCl molten salts, was reported recently [118]. ZnTe films with a smooth dense surface and particle diameters less than about 0.8 p,m were obtained, by properly adjusting the TeCU content and the reaction time. 

GP 2[ [R 3a[The sputtered silver on aluminum alloy (AlMg3) platelets, machined by thin-wire pEDM, were smooth and dense. On prolonged operation under reaction conditions, small silver particles are generated by surface diffusion so that also the blank aluminum platelet surface is exposed (20 vol.-% ethylene, 80 vol.-% oxygen 3 bar 0.23-2 s 250 °C) [43]. 

GP 2] [R 3a] The performance of one micro reactor with three kinds of catalyst -construction material silver, sputtered silver (dense) on aluminum alloy (AlMg3), and sputtered silver on anodically oxidized (porous) aluminum alloy (AlMg3) -was compared with three fixed beds with the same catalysts [44]. The fixed beds were built up by hackled silver foils, aluminum wires (silver sputtered) and hack-led aluminum foils (anodically oxidized and silver sputtered), all having the same catalytic surface area as the micro channels. Results were compared at the same flow rate per unit surface area. 

In Figure 3b and c the absolute atomic concentrations of carbon and silicon, respectively, are shown as a function of the carbon fraction. As expected, the carbon concentration increases upon alloying. In contrast, the silicon content decreases rapidly, which implies that the material becomes less dense. As it was reported that the Si—Si bond length does not change upon carbon alloying [116], it thus... 

Palladium-based dense metallic membranes have been known to be completely selective for hydrogen permeation and are used in commercially available small-scale hydrogen purification units (e.g., Johnson Matthey, 2007 REB Research, 2007 Power + Energy, 2007 ATI Wah Chang, 2007). These hydrogen purification units typically use palladium-alloy... 

Ion-beam thinning is usually used for dense bulk specimens where particular regions must be analyzed. It can be useful in AEM for thinning the same single crystals used in surface analysis to make direct comparisons with results from AES, XPS, etc. Ion-beam thinning can also be useful in analysis of interfaces and defects within bulk metallic catalysts such as Pt and Pd and their alloys. 

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