Ultrasonics dissolving metals

In addition to classical methods such as weight loss (via coupons), solution analysis for dissolved metal, monitoring of gas evolution (in the case of H2) and change in metal resistance, a select number of electrochemical techniques are widely accepted. This section briefly describes these methods. Weight-loss coupons are still the traditional, accepted baseline for comparisons electrical resistance (ER) and linear-polarization resistance (LPR) are the most widely used electrical and electrochemical techniques. Electrode potential monitoring is sometimes a valuable way of following active/passive transitions. There continues to be an emphasis on the use of non-destructive testing (NDT) techniques (particularly ultrasonic types). 

Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). 

The sonochemistry of solutes dissolved in organic Hquids also remains largely unexplored. The sonochemistry of metal carbonyl compounds is an exception (57). Detailed studies of these systems led to important mechanistic understandings of the nature of sonochemistry. A variety of unusual reactivity patterns have been observed during ultrasonic irradiation, including multiple ligand dissociation, novel metal cluster formation, and the initiation of homogeneous catalysis at low ambient temperature (57). 

Keeping in mind the above work, experiments were carried out to examine the effects of ultrasound, on the dissolution of zinc metal in an alkaline medium and the decomposition of zinc-dithizone complex in the presence of an ultrasonic field. To examine the effect of power ultrasound on the dissolution of zinc metal in alkaline media, 0.0480 g zinc metal was treated with 10 ml of 5 M NaOH solution. Two samples of this solution were exposed to ultrasound for 15 and 30 min, while, control samples were also kept in the similar condition and for the same duration. To compare their spectra and concentration of dissolved zinc in sonicated and control conditions, zinc-dithizone complex was formed by adding 0.5 ml of 0.005% dithizone solution. The red coloured complex, thus obtained, was extracted in chloroform and made upto to the mark in 25 ml volumetric flask with chloroform. 

The experimental system for measuring the sonoluminescence spectrum of alkali-metal atom emission from an aqueous solution is similar to that for measuring the MBSL spectrum from water. Degassing the solution is an important procedure because the presence of dissolved air affects the emission intensity. In an air-saturated solution, no observation of alkali-metal atom emission has been reported, whereas continuum emission can be observed. A typical experimental apparatus using ultrasonic standing waves is shown in Fig. 13.3 [8]. The cylindrical sample container is made of stainless steel, and its size is 46 mm in diameter and 150 mm in... 

USAL has also been used in the determination of trace impurities in high-purity materials. This type of analysis is mandatory with a view to controlling their quality and studying the synergistic action of, and correlation with, impurities. The accuracy and precision of the analytical results depend strongly on the particular separation procedure used before the determination step, as shown in the multi-element quantitative USAL of impurities such as iron, copper, lead and bismuth in high-purity silver metal. For this purpose, a silver sample was dissolved in nitric acid and treated with chloride, after which the solution was evaporated to dryness and the impurities were redistributed on the surfaces or in the interstitial spaces of agglomerates of matrix crystals. Then, the impurities were leached into 0.1 M nitric acid with the aid of ultrasonic irradiation [91]. 

The concentration of metals that are detrimental to catalysts added can vary between 20.0 ppm for Fe to 100 ppm for Ni and lOOOppm for V. The presence of these metals necessitates the need for analysis of these metals to determine their concentrations prior to the cracking process. The best method to analyse these oil samples needs to be rapid and accurate. Careful selection of the method either from experience or by trial and error may be applied depending on the metal and the concentration. Sample dissolution in a solvent or solvent mixture is considered the easiest but may not be suitable for low limits of detection. Destructive sample preparation methods, i.e. oxygen bomb combustion, microwave acid digestion followed by pre-concentrating may be required for trace analysis and/or with the aid of a hyphenated system, e.g. ultrasonic nebuliser. Samples prepared by destmctive methods are dissolved in aqueous solutions that have very low matrix and spectral interferences. 

The removal of unwanted air or gas is important in many food processes and it can be extremely difficult especially in very viscous liquids such as chocolate. Ultrasonically assisted degassing is particularly rapid in aqueous systems and can be used to remove any dissolved gas down to a very low level, thus is of great benefit in situations requiring the rapid and controlled removal of a gas or gases from a system. However ultrasound has also been employed to degas liquids as viscous as molten glass [73] and as dense as molten metals [74] during their solidification process. 

The kinetics of several well-known electrochemical reactions have been studied in the presence of an ultrasonic field by Altukhov et al. [142], The anodic polarization curves of Ag, Cu, Fe, Cd, and Zn in various solutions of HC1 and H2S04 and their salts were measured in an ultrasonic field at various intensities. The effect of the ultrasonic field on the reaction kinetics was found to be dependent on the mechanism of metal anodic dissolution, especially on the effect of this field on the rate-determining step of the reaction. The results showed that the limiting factor of the anodic dissolving of Cu and Ag is the diffusion of reaction products, while in the case of Fe it is the desorption of anions of solution from the anode surface, and at Cd the limiting factor is the rate of destruction of the crystal lattice. Similar results were obtained by Elliot et al. [ 143] who studied reaction geometry in the oxidation and reduction of an alkaline silver electrode. 

Japanese researchers [248] have designed an apparatus for the electrochemical reduction of carbon dioxide employing ultrasound. The apparatus comprises an electrolytic cell containing C02-dissolved electrolytic solution, a porous Pt-group metal anode, a proton-conductive solid electrolyte having a porous metal cathode used as a catalyst for the electrochemical reduction of COz on one side and a second anode on the other side facing oppositely to the cathode, and an ultrasonic vibrator. C02 can be reduced effectively for a long time. 

Active charcoal (AC) (Johnson Matthey, 5.0 g, dried at 100°C for 1 h) was utilized as a support. An ionic liquid ([N-bulyl-4-niethylpyridinium ] [tetrafluoroborate ], ([NBdMPy pFF]), Merck AG 98%, 0.51 g) was diluted with 10 ml of extra-dry acetone (Acros Organics) and the active metal species, Pd(II) acetylacetonate (Pd(acac)) (Aldrich, 99%, 0.050 g) was dissolved thereafter in 10 ml of extra-dry acetone. These solutions were mixed under magnetic stirring, additional 10 ml of extra-dry acetone was added and the solution was poured on the active charcoal, followed by a 30 s sonication in an ultrasonic bath. Finally, the mixture was placed in a rotary evaporator (Buchi R-124) and the solvent, acetone, was removed under vacuum (80°C, 19 mbar, 1 h) upon which the dissolved Pd -species is transferred to a Pd(TV) species... 

The conformations of the alkali metal complex of A A and of its c-2 symmetric analog are identical, and this holds also for their solid and dissolved state. Complexation, apparently, renders the structure rigid. For the uncomplexed cyclopeptides, however, it turned out by measurement of CD, ultrasonic absorption [47a] and, mainly, NMR spectroscopy [47b] that there is a fast conformational equilibrium between up to four individual molecules depending on the polarity of the solvents. The stability of one conformer will be directed i.a. by the competing formation of hydrogen bonds intramolecularly vs H-donors or acceptors in the solvents. The important question as to the bio-active conformation has not been strictly answered so far. 

K at a rate of 3 °C/hr, and quenched in ice water. The NaCl/KCl flux was dissolved in H2O using an ultrasonic bath. The starting metals were Ce 99.9%, AgM3N, and Sb 325 mesh, M2N5. 

Metal-organic frameworks can be synthesized with a wide variety of metal cations and a large choice of functionalized organic linkers by use of various synthesis methods, such as solvothermal (hydrothermal), microwave heating, ultrasonic, mechanochemical, electrochemical synthesis, and the spray-drying. However, only the conventional solvothermal (hydrothermal) method is well studied for MOF synthesis. In a typical solvothermal synthesis, both organic and inorganic precursors are dissolved in solvent... 

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