Solutions metallic

Atmospheric corrosion results from a metal s ambient-temperature reaction, with the earth s atmosphere as the corrosive environment. Atmospheric corrosion is electrochemical in nature, but differs from corrosion in aqueous solutions in that the electrochemical reactions occur under very thin layers of electrolyte on the metal surface. This influences the amount of oxygen present on the metal surface, since diffusion of oxygen from the atmosphere/electrolyte solution interface to the solution/metal interface is rapid. Atmospheric corrosion rates of metals are strongly influenced by moisture, temperature and presence of contaminants (e.g., NaCl, SO2,. ..). Hence, significantly different resistances to atmospheric corrosion are observed depending on the geographical location, whether mral, urban or marine. 

Powder Metallurgy Design Solutions, Metal Powder Industries Federation, Princeton, N.J., 1993. 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

Liquid Solution Metal plating effluent spent acids wash-waters... 

Cyan-kalium, n. potassium cyanide, -kalium-losung, /. potassium cyanide solution, -ko-balt, m. cobalt cyanide, -kohlensaure, / cyanocarbonic acid. -kupfer, n. copper cyanide, -laugerei, -laugung, /. cyaniding. cyanidation. -losung, / cyanide solution, -metall, n. metallic methyl cyanide, -natrium, n. sodium cyanide. -platin, n. platinum cyanide. 

Kali-kugel, /. potash bulb, -lauge, /. potash lye, caustic potash solution, -losung, /. potash solution, -metall, n. (metallic) potassium. -olivenolseife, /. potash olive oil soap, -praparat, n. potash (or potassium) preparation. -reibe,/. (Petro. ) potash series, -roh-salz, n. crude potassium salt, -salpeter, m. 

Rhodan-ion, n. thiocyanogen ion, CNS -kali, -kalium, n, potassium thiocyanate, -kalzium, n. calcium thiocyanate, -kupfer, n. cupric thiocyanate, copper(II) thiocyanate. -iSsung, /. thiocyanate solution, -metall, n. (metallic) thiocyanate, -methyl, n. methyl thiocyanate, -natrium, n, sodium thiocyanate, -nickel, m. nickel thiocyanate, -quecksilber, n. mercury thiocyanate, -salz, n. thiocyanate, -sdure, /. (Org. Chem.) thiocyan(at)o acid, -tonerde, /. aluminum thiocyanate. 

Butler and Ison S have suggested that variation in corrosion rate can be influenced by surface roughness, which allows a large number of nuclei for steam bubble formation. In these circumstances they have suggested that concentration of ions in solution next to the surface will be greater, and their observations on corrosion damage indicate that the steam bubbles may provide crevices or at least enhanced conditions for dissolution at the triple interface (solution/metal/steam). 

Oxygen from the atmosphere, dissolved in the electrolyte solution provides the cathode reactant in the corrosion process. Since the electrolyte solution is in the form of thin films or droplets, diffusion of oxygen from the atmosphere/electrolyte solution interface to the solution/metal interface is rapid. Moreover, convection currents within these thin films of solution may play a part in further decreasing concentration polarisation of this cathodic process . Oxygen may also oxidise soluble corrosion products to less soluble ones which form more or less protective barriers to further corrosion, e.g. the oxidation of ferrous species to the less soluble ferric forms in the rusting of iron and steel. 

Diffusion coatings are formed as a result of interaction of two distinct processes the solute metal is brought into contact with the surface of the solvent, and this is followed by diffusion proper which consists in the gradual absorption of the solute into the lattice of the solvent. 

It must be noted that the values of Dq and E are influenced by the concentration of the solute metal and also by the presence of alloying elements in the solvent. It has also been shown that the diffusion coefficient for a given solute is in inverse proportion to the melting point of the solvent. D is least for metals forming continuous series of solid solutions and for self-diffusion. 

Gas-phase deposition In this process, a halide of the solute metal is passed in vapour form over the surface of the metal to be coated, which is heated to a temperature at which diffusion can take place. Temperatures of 500-1 300°C or more can be used, depending on the particular system considered. Generally, filler atmospheres are provided to carry the halide vapour these atmospheres are usually reducing gases such as hydrogen, cracked ammonia, etc. or inert gases (helium, argon). 

It is difficult to point to the basic reason why the average-potential model is not better applicable to metallic solutions. Shimoji60 believes that a Lennard-Jones 6-12 potential is not adequate for metals and that a Morse potential would give better results when incorporated in the same kind of model. On the other hand, it is possible that the main trouble is that metal solutions do not obey a theorem of corresponding states. More specifically, the interaction eAB(r) may not be expressible by the same function as for the pure components because the solute is so strongly modified by the solvent. This point of view is supported by considerations of the electronic models of metal solutions.46 The idea that the solvent strongly modifies the solute metal is reached also through a consideration of the quasi-chemical theory applied to dilute solutions. This is the topic that we consider next. 

Alloys of metals tend to be stronger and have lower electrical conductivity than pure metals. In substitutional alloys, atoms of the solute metal take the place of some atoms of a metal of similar atomic radius. In interstitial alloys, atoms of the solute element fit into the interstices in a lattice formed by atoms of a metal with a larger atomic radius. 

Metal-Water and Ionic Solution-Metal Interphases... 

Metal-water and solution-metal interfaces is of primary importance since many electrochemical processes occur there that are relevant for electrocatalysis, corrosion. 

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.

When a liquid-liquid interface is to be investigated using an electrode in the more dense phase, or for studies at the water-air interface, a submarine electrode can be deployed [18,19,34], depicted schematically in Fig. 3(b). In this case, the electrode is inverted in the cell, such that the tip points upwards, and an insulated connection is made through the solution. Metal electrodes down to the nanometer scale can also be fabricated by sealing an etched Pt or Pt-Ir wire in a suitable insulating material, leaving just the etched end exposed [35-37]. 

The decrease in free energy (—AG) which provides the driving force in a cell may ensue either from a chemical reaction or from a physical change. In particular, one often studies cells in which the driving force is a change in concentration (almost always a dilution process). These cells are called concentration cells. The alteration in concentration can take place either in the electrolyte or in the electrodes. As examples of alterations in concentration in electrodes, mention may be made of amalgams or alloy electrodes with different concentrations of the solute metal and in gas electrodes with different pressures of the gas. 

Electrode-concentration is based on dilution of the electrode material itself. For the electrode material to be engaged in such a process, it must have a changeable concentration. Amalgams or alloy electrodes with different concentrations of solute metal, and gas elec-... 

In a typical reaction 100 - 200 mg of metal [Cr or Ni] was evaporated from a preformed alumina crucible over a period of 60 - 90 min and deposited into a mixture of 2 in poly(dimethylsiloxane) [Petrarch Systems 0.1 P.] within a rotary solution metal vapor reactor operating at 10 4 torr. The reaction flask was cooled to approximately 270 K by an iced-water bath. For a description of the apparatus see Chapter 3 of reference 4. The product in each case was a dark orange viscous liquid and was characterized as obtained from the reaction vessel. 

This impedance response, in general, is similar to that elicited from an Armstrong electrical circuit, shown in Figure 3, which we represent by Rfl+Cd/(Rt+Ca/Ra). Rfl is identified with the ohmic resistance of the solution, leads, etc. Cj with the double-layer capacitance of the solution/metal interface Rfc with its resistance to charge transfer and Ca and Ra with the capacitance and resistance... 

In contrast to a mixture of redox couples that rapidly reach thermodynamic equilibrium because of fast reaction kinetics, e.g., a mixture of Fe2+/Fe3+ and Ce3+/ Ce4+, due to the slow kinetics of the electroless reaction, the two (sometimes more) couples in a standard electroless solution are not in equilibrium. Nonequilibrium systems of the latter kind were known in the past as polyelectrode systems [18, 19]. Electroless solutions are by their nature thermodyamically prone to reaction between the metal ions and reductant, which is facilitated by a heterogeneous catalyst. In properly formulated electroless solutions, metal ions are complexed, a buffer maintains solution pH, and solution stabilizers, which are normally catalytic poisons, are often employed. The latter adsorb on extraneous catalytically active sites, whether particles in solution, or sites on mechanical components of the deposition system/ container, to inhibit deposition reactions. With proper maintenance, electroless solutions may operate for periods of months at elevated temperatures, and exhibit minimal extraneous metal deposition. 

In aqueous solutions, metal ions interact with and are bound to H20 molecules. Thus, in such solutions, Ni2+ should more accurately be represented as the aquo-metal ion [Ni(H20)6]2+. Aquometal ions tend to be acidic, and have a tendency to hydrolyze ... 

The electron transfer at the solution-metal interface it is not forced to occur through an external circuit where it would produce useful electrical energy. 

Selective precipitants for quadrivalent metals in acid solution. Metals weighed as dioxides. 

Zn Zn2+ Cu2+ Cu. This battery comprised two concentric terracotta pots, the outer pot containing a zinc solution and the inner pot containing a copper solution. Metallic rods of copper and... 

A metallic electrode consisting of a pure metal in contact with an analyte solution develops an electric potential in response to a redox reaction occurring at its metal surface. Common metal electrodes such as platinum, gold, palladium or carbon are known as inert metal electrodes whose sole function is to transfer electrons to or from species in solution. Metal electrodes corresponding to the first kind are pure metal electrodes such as Ag, Hg and others that respond directly to a change in activity of the metal cation in the solution. For example, for the reaction... 

---