Dissolution phenomena

Yasuda K, Taniguchi A, Akita T, loroi T, Siroma Z. 2006a. Characteristics of a platinum black catalyst layer with regard to platinum dissolution phenomena in a membrane electrode assembly. J Electrochem Soc 153 A1599-A1603. 

Dissolution film models, though conceptually simple and instructive, are inherently unsatisfying in their application to complex dissolution phenomena or systems. 

Figure 4. The temperature-electrolyte concentration diagram, defining regions of different anodic dissolution phenomena, according to Fukushima et al9...

Novolac resins, as the oldest synthetic polymers, have played an important role 1n microelectronic Industry as positive photoresists. Studies of novolac dissolution have populated the literature a recent survey shows that the rate of dissolution 1s influenced by the concentration of the alkali, size of the cation, addition of salt, and the presence of dissolution Inhibitors (1-6). The voluminous experimental results, however, have not led to a clear understanding of the dissolution phenomena. Arcus (3) proposed an 1on-permeab1e membrane" model while Szmanda (1) and Hanabata (6) emphasized the Importance of secondary structures of novolac molecules, for Instance, Inter- or Intramolecular hydrogen bonding and the various isomeric configurations of the resins. These important contributions nevertheless point to a need for additional studies of the mechanism of dissolution. 

Reactions M-O represent incongruent dissolution of Ca(OH)2s because the solubility of CaCOjS is much smaller than the solubility of Ca(OH)2s (Table 2.7). Therefore, introduction of Ca(OH)2s to water in equilibrium with atmospheric C02 leads to spontaneous formation of CaC03s. The well-known incongruent dissolution phenomena are those representing the dissolution of aluminosilicate minerals. For example, K-feldspars (orthoclase) undergo incongruent dissolution when exposed to water and carbonic acid to form kaolinite ... 

In the majority of dissolution phenomena, the solvation step is almost instantaneous. The diffusion process is much slower and, therefore constitutes the rate limiting step. Noyes and Whitney (1897) developed an equation based on Pick s second law of diffusion to describe dissolution within the scope of their model, and report the relation ... 

Beyond this effect, however, the concentration gradients measured in various solid-phase metal fractions at the soil-root interface can also be attributed to the effects of a variety of processes, such as rhizosphere acidification or alka-linization, adsorption or desorption reactions, and precipitation or dissolution phenomena, which are themselves associated with plant uptake and a range of... 

Of course geochemistry is often concerned with "geological" time scales, but this is not necessarily so. Many relevant data are to be found in ref.50. To give orders of magrutude for support oxides, the half-life of a surface A1 is 669 days (5.8 10 s) for aAl203, but only 44 days (3.8 10 s) for 8Al203. As we will discuss in IV.B, the presence of TMC ions may speed up dissolution phenomena. In the case of [MgII(H20)6j/SiC>2, the time scale for dissolution/repredpitation was t5 ically a few tens of hours, or lO s , ... 

In a fiirther series of experiments, phosphotungstic acid (PWA) was impregnated onto silica particles and the resulting material was loaded in the recast Nafion. As is well known, heteropolyacids (HPAs) have demonstrated suitable characteristics to be used as proton conductive materials in fuel cells [4-6]. Due to dissolution phenomena in water, however, previous experiments using solid heteropolyacid did not result in stable fuel cell performance [5]. To overcome this problem, resulting in a short lifetime of the fuel cell, experiments of blocking the HPA in a host material were carried out [7-9]. Thus, in this work the phosphotungstic acid-modified membrane was compared, in terms of performance, with the bare silica-recast Nafion membrane in direct methanol fuel cell at 145°C. 

Precipitation and dissolution phenomena are extremely important in both natural waters and water treatment processes. Dissolution of minerals is a prime factor in determining the chemical composition of natural waters. Natural water chemical composition can be altered by precipitation of minerals and the subsequent sedimentation of these solids from supersaturated solutions. Water and wastewater treatment processes such as lime-soda softening, iron removal, coagulation with hydrolyzing metal salts, and phosphate precipitation are based on precipitation phenomena. 

Precipitation and dissolution phenomena become more complicated if the cation of the salt is a weak acid, such as NH4, or if the anion is a weak base, such as CN or COg . AgCN(s), for example, dissolves as follows ... 

Percolation theory helps explain some dissolution phenomena. Unfortunately, it does not explain why the dissolution rate is molecular weight dependent nor why different monomeric species inhibit novolac with different efficiencies. 

The Probabilistic Approach allows for the explanation many previously unexplained dissolution phenomena the effect of added salts (7), the MW dependence (5) and the effect of residual casting solvent (35,3d) on the dissolution rate. 

The presence of a wide spectrum of amorphous and crystalline regions in crystalline polymers gives a combination of dissolution phenomena. Amorphous regions in LDPE or PP can contain whole polymer chains which can be slowly leached into a good solvent, such as xylene, even at room temperature. However, the amorphous regions tend to be fairly small, and the polymer will maintain its structural integrity until the dissolution temperature approaches... 

Polymer solutions are obtained by complete dissolution of the macromolecule into a solvent. As in any case of dissolution of a solute in a solvent, dissolution phenomena are controlled by the balance between, on the one hand, solute-solute and solvent-solvent interaction forces and, on the other hand, solute-solvent interaction forces. Thus, general thermodynamic considerations, including solubility parameters and cohesive energy density notions, can help us to predict whether or not a polymer can be soluble in a given solvent. Nevertheless, solubilisation of a polymer in a suitable solvent is a more complex phenomenon than solubilisation of a small molecule, and it generally takes a long time because it requires several steps. 

For the last decade the growing extension of Madrid has led to the construction of housing and industrial estates to the east and southeast of the city centre. The terrain in these areas is chiefly gypsum rock affected by dissolution phenomena, covered with clayey material. 

The electrolyte s role in the degradation of the active material, in particular in the metal s dissolution phenomena, has already been mentioned for layered oxides. This results from the degradation of the organic electrolyte accompanied by the formation of radical or acid species (HF), the latter being responsible for the dissolution of the material. Since manganese is the transition metal most sensitive to the dissolution phenomena, it can be observed that the spinel LiMn204 is particularly affected by this dissolution concern, according to the mechanism [AUR 99, WHO 04] ... 

More detailed surface features and topography can be revealed by scanning tunneling microscopy (STM) or atomic force microscopy (AFM). The instruments employing these techniques are capable of resolution at the atomic level. Recent efforts have also shown the feasibility of manipulating and rearranging atoms on the surface. The techniques do not require vacuum and can even be used in solution to study such processes as reactions taking place at the surfaces of electrodes, corrosion, or precipitation/dissolution phenomena. 

Non exclusively Current-Voltage Techniques In this class of techniques one handles an extraexperimental parameter (either excitation or response) in order to obtain additional information relevant to nonelectrical aspects of the dissolution phenomena. 

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