Aqueous metal salts

The strong influence of morphology and mixing is well illustrated with the composite particle investigation. These particles were composed of a nickel shell coated on spherical aluminum particles by hydrogen reduction in aqueous metal salt solution. The overall ratio of material in a particle was about 80 wt% Ni and 20 wt% aluminum. With these particles, the ratio of reactants was approximately the same as in the mixed powders, but the morphology of the reactants is radically different. 

We have hitherto dealt with the complexation thermodynamics in the homogeneous solutions. However, the above interpretation based on the linear enthalpy-entropy relationship may be extended to the complexation behavior in the solvent extraction of aqueous metal salts with ionophores in organic solvent. 

Direct interactions of aqueous metal salt solutions with bases failed, as a rule, to yield uniform particles thus, it was necessary to design some other approaches to achieve such dispersions. The fundamental ideas were based on the fact that seldom, if ever, can a metal ion in an aqueous solution be directly converted to an oxide. Instead, the initial steps involve the formation of metal hydroxides or oxyhydroxides. Either these products remain stable as precipitated, or they convert to oxides on aging by processes that may take different lengths of time but that can be accelerated by various dehydration methods. Consequently, metal ion hydrolysis... 

Reduction of suitable aqueous metal salts by electroless plating yields metal-coated mica pigments. They are less expensive than noble metal flakes (Au, Ag) and their brilliant metallic appearance is comparable with that of metallic flakes [5.192], [5.193],... 

Diffraction data for concentrated aqueous metal salt solutions containing noncomplex-forming anions have been used to derive structures... 

Using urea (CO(NH2)2) makes it possible to employ the real procedure of DP as first described.2,3 Urea acts as a delay base since there is no reaction when it is dissolved in a suspension of the support in the aqueous metal salt solution at room temperature hydrolysis only occurs when this is heated above 333 K, according to the equation ... 

Layered double hydroxides (LDHs), also known as anionic clays and hydro-talcite-like materials, are layered solids that are of increasing interest [5-8]. They consist of stacks of positively charged hydroxide layers with interlayer, charge-balancing, anions and are available as naturally occurring minerals [9] and as synthetic materials. They were prepared in the laboratory in 1942 when Feitknecht reacted dilute aqueous metal salt solutions with base [10, 11], although the first detailed structural analyses of LDHs were not performed until the late 1960s by Allmann and Taylor and their co-workers [12-15]. 

Chemical Treatment of Paper. Test samples were treated with aqueous copper(II) or iron(II) sulfate solutions or with nonaqueous copper(II) or iron(III) acetylacetonate solutions. All chemical treatments were designed to obtain extensive and uniform penetration into the paper structure. To facilitate contact between paper and solution and to provide physical support, test samples were interleaved with fibrous sheets of nonwoven polyester. Sorption of metal species from aqueous media was achieved by immersion of paper samples into the solution of choice for 16-18 h. The metal-catalyst content of paper was varied by adjusting the solution concentration. The concentration ol the aqueous metal salt solutions was varied from 10 3 to 10 1 M. One liter of solution was used for every 25 sheets of paper. At the end of the treatment period, paper samples treated in aqueous media were washed with water. 

Complexation of metal ions with the carboxyl resin Complexation of the carboxyl resin was carried out towards Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions by a batch equilibration technique. A quantity (100 mg) of the resin was stirred in an aqueous metal salt solution (0.05 mol L , 50 mL) for 24 h. The complexed resins were collected by filtration and washed with distilled water to remove uncomplexed metal ions. The concentrations of the metal salt solutions were estimated by UV spectrophotometric methods. 

The extractants that are used to form oiganic-soluble metal species from aqueous metal salts usually are grouped into three classes according to the type of reaction that occurs. Solvating extractants compete with water in coordination bonds around a metal ion and cany neutral salts into the organic phase. Cation... 

Virtually no metal extraction system involves only one reaction. In aqueous metal salt solutions there occur homogeneous association and complexation reactions that make true species concentrations differ Aom the analytical concentrations that are measured and that enter into material balances. In sulfate solutions bisuifate formation occurs at low pH, and metai-sulfate ion pairing may take place. In chloride and amnaonia solutions metal complexation is common. Dimerization and other association reactions often occur in the organic phases. And two-phase extraction reactions of acids or other species may take place simultaneously with metal extraction or stripping. The equilibria of these reactions must be modeled concurrently with the... 

Metal ions can be introduced into the flame by injecting an aerosol of the appropriate aqueous metal salt. The metal ions can be present in the flame as M+, M+-H20 or M+ 2H2O. When considering the electrochemistry here it is important to realize that, in the flame plasma, the mobility of the electrons in much higher than that of the ions (by a factor of 1000). For example, the mobilities of Cs and H30" in the flame plasma are 5.0 cm s and 8.0 cm s respectively, whereas the mobility for electrons is 4000 cm2 y-i -1 [ 5] ... 

Chemical precipitation of metal from a solution of a soluble salt may also be used to form metallic powders. In this procedure, a reducing agent such as sodium borohydride is added to an aqueous metal salt, MX (Eq. 14). A mixture of aqueous products will be produced in addition to the reduced metal, since sodium borohydride also reacts exothermically with water to yield borax, Na2B207. As we will see in Chapter 6, this is the most widely used procedure for the synthesis of nanoparticulate metals, from the reduction of metal salts confined within nanosized entrainer molecules. 

Figure 5 shows a typical experimental apparatus used. An aqueous metal salt solution is first prepared and fed into the apparatus in one stream. In another stream, distilled water is pressurized and then heated to a temperature above the desired reaction temperature. The pressurized metal salt solution stream and the pure supercritical water stream are then combined at a mixing point, which leads to rapid heating and subsequent reactions in the reactor. After the solution leaves the reactor, it is rapidly quenched. In-line filters are used to remove larger particles. Pressure is controlled with a back-pressure regulator. Fine particles are collected in the effluent. By this rapid heating method, the effect of the heating period on the hydrothermal synthesis is eliminated thus, specific features of supercritical hydrothermal synthesis can be elucidated. 

Another flow technique was developed by Adschiri and Aral, who explored the continuous hydrothermal synthesis of fine metal oxide particles using supercritical water (see Chapter 8). In this process, the aqueous metal salt solutions are rapidly heated by combining with a stream of supercritical water. After the... 

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