Pure metals

The viscosity coefficients at dislocation cores can be measured either from direct observations of dislocation motion, or from ultrasonic measurements of internal friction. Some directly measured viscosities for pure metals are given in Table 4.1. Viscosities can also be measured indirectly from internal friction studies. There is consistency between the two types of measurement, and they are all quite small, being 1-10% of the viscosities of liquid metals at their melting points. It may be concluded that hardnesses (flow stresses) of pure 

Metal Temperature (K) Viscous Damping Constant Reference 

These data show clearly that that the intrinsic behavior in pure metals is visco-elastic with the velocity proportional to the applied stress (Newtonian viscosity). Although there is a large literature that speaks of a quasi-static Peierls-Nabarro stress, this is a fiction, probably resulting from studying of insufficiently pure metals. 

In impure metals, dislocation motion ocures in a stick-slip mode. Between impurities (or other point defects) slip occurs, that is, fast motion limited only by viscous drag. At impurities, which are usually bound internally and to the surrounding matrix by covalent bonds, dislocations get stuck. At low temperatures, they can only become freed by a quantum mechanical tunneling process driven by stress. Thus this part of the process is mechanically, not thermally, driven. The description of the tunneling rate has the form of Equation (4.3). Overall, the motion has two parts the viscous part and the tunneling part. 

From an electrocatalytic point of view, it is almost an ultimate aim of research and development in this field to find electrode materials which have 

Understanding of these factors is not yet sufficiently conclusive. Among various difficulties, there is the lack of a solid basis for the operative HER mechanisms on these metals. Certainly, one must be sure beforehand in an analysis of this kind that the electrocatalytic activities of various metals can 

In contrast to the electronic properties discussed above, structural factors in electrocatalytic activity have been investigated by several authors. In spite of the extreme difficulty in this kind of work to maintain an unperturbed surface state, free of surface contamination, and to reproduce a defined surface, some interesting results have been reported. 

Using single-, as well as poly-, crystalline Pt electrodes in 0.5 M H2SO4, Bagotzky et have reported that 17 at a constant cathodic current is 

Mechanical deformation was effective in decreasing 17 on the (100) face of Cu or, to some extent, on but had no significant effect on 

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Metals A and B form an alloy or solid solution. To take a hypothetical case, suppose that the structure is simple cubic, so that each interior atom has six nearest neighbors and each surface atom has five. A particular alloy has a bulk mole fraction XA = 0.50, the side of the unit cell is 4.0 A, and the energies of vaporization Ea and Eb are 30 and 35 kcal/mol for the respective pure metals. The A—A bond energy is aa and the B—B bond energy is bb assume that ab = j( aa + bb)- Calculate the surface energy as a function of surface composition. What should the surface composition be at 0 K In what direction should it change on heaf)pg, and why ... 

Surface heterogeneity may merely be a reflection of different types of chemisorption and chemisorption sites, as in the examples of Figs. XVIII-9 and XVIII-10. The presence of various crystal planes, as in powders, leads to heterogeneous adsorption behavior the effect may vary with particle size, as in the case of O2 on Pd [107]. Heterogeneity may be deliberate many catalysts consist of combinations of active surfaces, such as bimetallic alloys. In this last case, the surface properties may be intermediate between those of the pure metals (but one component may be in surface excess as with any solution) or they may be distinctly different. In this last case, one speaks of various effects ensemble, dilution, ligand, and kinetic (see Ref. 108 for details). 

Allen G L ef a/1986 Small particle melting of pure metals Thin Solid Films 144 297... 

In a pure metal the atoms of the solid are arranged in closely packed layers. There is more than one way of achieving close packing but it... 

The interstitial carbides These are formed by the transition metals (e.g. titanium, iron) and have the general formula M, C. They are often non-stoichiometric—the carbon atoms can occupy some or all of the small spaces between the larger metal atoms, the arrangement of which remains essentially the same as in the pure metal (cf. the interstitial hydrides). 

Manganese is the third most abundant transition metal, and is widely distributed in the earth s crust. The most important ore is pyrolusite, manganese(IV) oxide. Reduction of this ore by heating with aluminium gives an explosive reaction, and the oxide Mn304 must be used to obtain the metal. The latter is purified by distillation in vacuo just above its melting point (1517 K) the pure metal can also he obtained by electrolysis of aqueous manganese(II) sulphate. 

The silver salts of most carboxylic acids are only sparingly soluble in cold water, and hence are readily prepared. Moreover they very rarely contain water of crystallisation, and therefore when dried can be analysed without further treatment. The analysis itself is simple, rapid and accurate, because gentle ignition of a weighed quantity of the silver salt in a crucible drives off the organic matter, leaving a residue of pure metallic silver. 

Taconite is becoming increasingly important as a commercial ore. The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals. 

Manganese metal is ferromagnetic only after special treatment. The pure metal exists in four... 

Discovered by Gregor in 1791 named by Klaproth in 1795. Impure titanium was prepared by Nilson and Pettersson in 1887 however, the pure metal (99.9%) was not made until 1910 by Hunter by heating TiCk with sodium in a steel bomb. 

It is available in ultra pure form. Indium is a very soft, silvery-white metal with a brilliant luster. The pure metal gives a high-pitched "cry" when bent. It wets glass, as does gallium. 

L. radius, ray) Radium was discovered in 1898 by Mme. Curie in the pitchblende or uraninite of North Bohemia, where it occurs. There is about 1 g of radium in 7 tons of pitchblende. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride, employing a mercury cathode on distillation in an atmosphere of hydrogen this amalgam yielded the pure metal. 

Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife. 

Europe) In 1890 Boisbaudran obtained basic fractions from samarium-gadolinium concentrates which had spark spectral lines not accounted for by samarium or gadolinium. These lines subsequently have been shown to belong to europium. The discovery of europium is generally credited to Demarcay, who separated the rare earth in reasonably pure form in 1901. The pure metal was not isolated until recent years. 

Lithium containing 0.5-1% of sodium should be used the very pure metal reacts sluggishly and gives lower yields. 

Copper. The recovery of copper [7440-50-8] Cu, from ore leach Hquors as a stage in the hydrometallurgical route to the pure metal is one of the... 

Another use for cryoHte is in the production of pure metal by electrolytic refining. A high density electrolyte capable of floating Hquid aluminum is needed, and compositions are used containing cryoHte with barium fluoride to raise the density, and aluminum fluoride to raise the current efficiency. 

Gold [7440-57-5] Au, is presumably the first metal known and used by humans. It occurs ia nature as a highly pure metal and is treasured because of its color, its extraordinary ductility, and its resistance to corrosion. Early uses ia medicine and dentistry date to the ancient Chinese and Egyptians. In the Middle Ages the demand for gold led to the iatense, unsuccesshil efforts of alchemists to convert base metals iato gold. These pursuits became the basis for chemical science. The search for gold has been an important factor ia world exploration and the development of world trade. 

MohsAn early (1822) hardness comparison test involved assigning a relative number to aH known materials (usuaHy minerals and pure metals) by virtue of their relative abHity to scratch one another. The results of this classification are not relatable to other properties of materials or to other measures of hardness. As a result of this limited useflilness, the Mohs hardness test is primarily used for mineral identification. Some examples of the Mohs hardness scale, which ranks materials from 1 to 10, are Hsted in Table 6. 

Hydrogen reacts direcdy with a number of metallic elements to form hydrides (qv). The ionic or saline hydrides ate formed from the reaction of hydrogen with the alkali metals and with some of the alkaline-eartb metals. The saline hydrides ate salt-like in character and contain the hydride, ie,, ion. Saline hydrides form when pure metals and H2 react at elevated temperatures (300—700°C). Examples of these reactions ate... 

In neutral and alkaline environments, the magnesium hydroxide product can form a surface film which offers considerable protection to the pure metal or its common alloys. Electron diffraction studies of the film formed ia humid air iadicate that it is amorphous, with the oxidation rate reported to be less than 0.01 /rni/yr. If the humidity level is sufficiently high, so that condensation occurs on the surface of the sample, the amorphous film is found to contain at least some crystalline magnesium hydroxide (bmcite). The crystalline magnesium hydroxide is also protective ia deionized water at room temperature. The aeration of the water has Httie or no measurable effect on the corrosion resistance. However, as the water temperature is iacreased to 100°C, the protective capacity of the film begias to erode, particularly ia the presence of certain cathodic contaminants ia either the metal or the water (121,122). 

Properties and Selection of Nonferrous Alloys and Pure Metals" in Metals Handbook, 10th ed., American Society for Metals, Metals Park, Ohio, 1990. 

Usually, the ore or concentrate cannot be reduced to the metal in a single operation. An additional preparation process is needed to modify the physical or chemical properties of the raw material prior to its reduction. Furthermore, most pyrometaHurgical reductions do not yield a pure metal and an additional step, refining, is needed to achieve the chemical purity that is specified for the commercial use of the metal. 

Chlorination. In some instances, the extraction of a pure metal is more easily achieved from the chloride than from the oxide. Oxide ores and concentrates react at high temperature with chlorine gas to produce volatile chlorides of the metal. This reaction can be used for common nonferrous metals, but it is particularly useful for refractory metals like titanium (see Titanium and titanium alloys) and 2irconium (see Zirconium and zirconium compounds), and for reactive metals like aluminum. 

Nitriding Metals or Metal Hydrides. Metals or metal hydrides may be nitrided using nitrogen or ammonia. Pure metal powders or pure metal hydride powders yield nitride products that are nearly as pure as the precursors. 

Biomaterials. Just as stem designs have evolved in an effort to develop an optimal combination of specifications, so have the types of metals and alloys employed in the constmction of total joint implants. Pure metals are usually too soft to be used in prosthesis. Therefore, alloys which exhibit improved characteristics of fatigue strength, tensile strength, ductihty, modulus of elasticity, hardness, resistance to corrosion, and biocompatibiUty are used. 

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