Selective metallation

The enhanced strength and corrosion properties of duplex stainless steels depend on maintaining equal amounts of the austenite and ferrite phases. The welding thermal cycle can dismpt this balance therefore, proper weld-parameter and filler metal selection is essential. Precipitation-hardened stainless steels derive their additional strength from alloy precipitates in an austenitic or martensitic stainless steel matrix. To obtain weld properties neat those of the base metal, these steels are heat treated after welding. 

Liquid metal selection is usually limited to the lower melting point metals in Table 15. Figure 17 shows that Hquid metal viscosity generally is similar to water at room temperature and approaches the viscosities of gases at high temperature. Hydrodynamic load capacity with both Hquid metals and water in a bearing is about 1/10 of that with oil, as indicated in Table 2. 

Other methods of metal powder manufacture are also employed for specific metals. Selective corrosion of carbide-rich grain boundaries in stainless steel, a process called intergranular corrosion, also yields a powder. 

It is often found that wet corrosion attacks metals selectively as well as, or instead of, uniformly, and this can lead to component failure much more rapidly and insidiously than one might infer from average corrosion rates (Fig. 23.7). Stress and corrosion... 

The cost of resins is a major consideration. Heavy-metal-selective chelating resins are the most expensive. Table 4 provides some cost ranges for commercially available resins. 

B. Volesky, Advances in biosorption of metals Selection of biomass type. FEMS Microbiology reviews, 14, 291-301(1994). 

C20-0037. In each of the following pairs of transition metals, select the one with the higher value for the indicated property and give the reason (a) melting points of Pd and Cd (b) densities of Cu and Au and (c) first ionization energies of Cr and Co. 

C20-0038. In each of the following pairs of transition metals, select the one with the higher value for the... 

The presence of hydroxyaluminum- and hydroxyaluminosilicate polymer in interlayered montmorillonite greatly promotes the adsorption of Cd, Zn, and Pb (Saha et al., 2001). The adsorption selectivity sequences of montmorillonite (Pb > Zn > Cd) and interlayered montmorillonite (Pb Zn Cd) resemble the metal selectivity on amorphous Fe and Al hydroxides (Saha et al., 2001). On montmorillonite, the metals are predominantly adsorbed on the permanent charge sites in an easily replaceable state. However, a substantial involvement of the edge OH" groups of montmorillonite in specific adsorption of the metals is also observed, especially at higher pH (Saha et al., 2001). 

Davis, T.A., Llanes, F., Volesky, B. and Mucci, A. (2003) Metal selectivity of Sargassum spp. And their alginates in relation to their a-L-guluronic acid content and conformation. Environmental Science S. Technology, 37, 261-267. 

Two examples of pyrimidines 57, 58 were included in a study of direct magnesiation of heterocycles. Both of these metallated selectively at C-4 using inverse addition i.e. substrate added to the metallating agent <06AG(I)2958>. 

In addition to these homometallic (rhodium) clusters, several hetero-metallic clusters of the type [M M CO o]2, where M and M1 are each different metals selected from the Co, Rh, Ir triad (jc = 1-11), have been described and claimed to be useful catalysts in the reaction between carbon monoxide and hydrogen to produce oxygenated products (68, 69). These complexes can be prepared from the heterometallic dodecacar-bonyl complexes, [MuM (CO)12] (M, M1 = Co, Rh, or Ir y = 1-3), by simply mixing the appropriate dodecacarbonyl species in THF under nitrogen and then adding water (70). They can be isolated by adding a suitable cation e.g., Al3+, Mg2+, Ca2+, etc. 

Assuming that log P should be at least 5 for an essentially quantitative separation by a single extraction (see p. 57), ApH1/2 should be 5, 2.5 and 1.7 respectively for pairs of mono-, di- and trivalent metals. Selectivity by pH control is greatest, therefore, for trivalent metals and least for monovalent. This is reflected in the slopes of the curves which are determined by n and decrease in the order M3+ > M2+ > M+. 

Although there are no universal rules for metal selectivity as it depends on numerous factors, the obtained sequence is in agreement with the results reported in literature for the Kd sorption values on fresh precipitates of hydrous ferric oxide (Dzombak Morel 1990 Munk et al. 2002). The lowest factor observed for Mn comes in agreement with the well-known difficulty to remove this metal from mine waters due to its high solubility over a wide pH range (e.g., Hedin etal. 1994). 

Deriving Biogeochemical Parameters for Critical Loads of Heavy Metals Selection of a Receptor of Concern... 

Blood, tissues, intestinal content, bone, hair, nails Metals Selective tests AAS Mineralization (wet, dry) AAS ICP-MS... 

Reduction of benzyl ethers. Benzyl ethers are cleaved in high yield by calcium (2 equiv.) in liquid ammonia. By proper control of the amount of metal, selective reduction of benzyl ethers is possible in the presence of a triple bond or a t-butyldimethylsilyl ether group. However, there is little selectivity between benzyl ethers and thiophenyl, epoxide, or keto groups in this reduction. 

Skeletal (Raney ) catalysts are made by a very simple technique. An alloy of two metals in roughly equal proportions, where one metal is the desired catalytic material, and the other is dissolvable in hydroxide, is first made. This alloy is crashed and leached in concentrated hydroxide solution. The soluble metal selectively dissolves, leaving behind a highly porous spongelike structure of the desired catalytic metal. Catalysts formed by this technique show high activity and selectivity, and have found wide use in industry, particularly for hydrogenation and dehydrogenation reactions. 

Table 5.3. Alkali metals selected atomic and physical properties.

Table 5.7. Alkaline earth metals selected physical properties.

Remarks on the alloy crystal chemistry of the 4th group metals. Selected groups of isostructural phases, pertaining to simple common structural types have been collected in Table 5.25. A number of them (for instance CsCl, AuCu types, Laves phases, AuCu3 type) correspond to more or less extended solid solution... 

Atomic absorption and inductively coupled plasma spectrometers are metal-selective spectrometers used for organic metal analysis. The connection of these spectroscopic instruments to a liquid chromatograph is relatively simple. Chromatograms of alkylmercury3 and aminoplatinum analytes4 are shown in Figures 2.8 and 2.9, respectively. 

Solvent extraction has become a common technique for the determination of formation constants, P , of aqneons hydrophilic metal complexes of type MX , particularly in the case when the metal is only available in trace concentrations, as the distribntion can easily be measnred with radioactive techniques (see also section 4.15). The method reqnires the formation of an extractable complex of the metal ion, which, in the simplest and most commonly used case, is an nn-charged lipophilic complex of type MA. The metal-organic complex MA serves as a probe for the concentration of metal ions in the aqueous phase through its equilibrium with the free section 4.8.2. This same principle is used in the design of metal selective electrodes (see Chapter 15). Extractants typically used for this purpose are P-diketones like acetylacetone (HAA) or thenoyltrifluoroacteone (TTA), and weak large organic acids like dinonyl naph-talene sulphonic acid (DNNA). 

The ability to transfer the desired metal selectively across the aqueous-organic interface in both directions... 

TABLE 6. Alkali metal selectivities of lariat ethers 9a-9k measured by ESI in chloroform-methanol (1 19). Reproduced with permission from Ref. 44... 

Alloying of an active with an inactive metal selectively suppresses the reactions requiring the biggest ensembles. Interesting results can also in principle be obtained with alloys of two active metals when these metals behave sufficiently different in catalytic reactions. 

The experimental design was devoted to study the sample treatment in order to develop a model to remove metals selectively from water using resins (3 factors were considered)... 

The production of industrially important perfluoroalkane sulfonic acids is generally accomplished by electrochemical fluorination. This method of preparation remains expensive and proceeds in good yields only for short hydrocarbon chains.30 Recently however, Wakselman and Tordeux have described a chemical method for the preparation of trifluoromethane sulfonic acid.31 The procedure involves reaction of a metal selected from zinc, cadmium, manganese, and aluminum with sulfur dioxide in DMF, followed by the introduction of trifluoromethyl bromide under slight pressure. The intermediate sulfinate is subsequently oxidized by hydrogen peroxide, and then hydrolyzed which leads to formation of the trifluoromethane sulfonic acid. Successful extension of the sulfination process to the modification of PCTFE should result in the formation of a sulfinated polymer which can ultimately be oxidized to give a sulfonic-acid modified polymer. 

The most versatile reagent of this group is diethyldithiocarbamic acid (40), which forms coloured and extractable complexes with very many metals, selectivity being assured by control of the pH and the presence of masking agents.52 Here again the practical disadvantages stem from the ease of oxidation and many alternate carbamic acids derived from pyrrolidine and other dialkylamines have been studied. 

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