Dissolution solution process

X 10 mol/L in 8 Mpotassium hydroxide at room temperature. In general it is believ ed tliat tlie solution process consists of anodic dissolution of cadmium ions in tlie form of complex hydroxides (see Cadmium compounds). 

Dissolution/reprecipitation processes were evaluated for the recycling of poly-epsilon-caprolactam (PA6) and polyhexamethyleneadipamide (PA66). The process involved solution of the polyamide in an appropriate solvent, precipitation by the addition of a non-solvent, and recovery of the polymer by washing and drying. Dimethylsulphoxide was used as the solvent for PA6, and formic acid for PA66, and methylethylketone was used as the non-solvent for both polymers. The recycled polymers were evaluated by determination of molecular weight, crystallinity and grain size. Excellent recoveries were achieved, with no deterioration in the polymer properties. 33 refs. 

The comparison of I —> N and N —> I may also be explained by the buffered pH in the diffusion layer and leads to an interesting comparison between a process under kinetic control versus one under thermodynamic control. Because the bulk solution in process N —> I favors formation of the ionized species, a much larger quantity of drug could be dissolved in the N —> I solvent if the dissolution process were allowed to reach equilibrium. However, the dissolution rate will be controlled by the solubility in the diffusion layer accordingly, faster dissolution of the salt in the buffered diffusion layer (process I—>N) would be expected. In comparing N—>1 and N —> N, or I —> N and I —> I, the pH of the diffusion layer is identical in each set, and the differences in dissolution rate must be explained either by the size of the diffusion layer or by the concentration gradient of drug between the diffusion and the bulk solution. It is probably safe to assume that a diffusion layer at a different pH than that of the bulk solution is thinner than a diffusion layer at the same pH because of the acid-base interaction at the interface. In addition, when the bulk solution is at a different pH than that of the diffusion layer, the bulk solution will act as a sink and Cg can be eliminated from Eqs. (1), (3), and (4). Both a decrease in the h and Cg terms in Eqs. (1), (3), and (4) favor faster dissolution in processes N —> I and I —> N as opposed to N —> N and I —> I, respectively. 

Let us consider the dissolution-precipitation process in seawater in the following example. The normal concentrations of calcium and of carbonate in the near-surface oceanic waters are about [Ca2+] = 0.01 and [C032-] 2 x lO"4 M. The CaC03 in solution is metastable and roughly 2U0% saturated (1). Should precipitation occur due to an abundance of nuclei, TC032-] will drop to 10-4 M but [Ca2+] will change by no more than 2%. Therefore, the ionic strength of the ionic medium seawater will remain essentially constant at 0.7 M. The major ion composition will also remain constant. We shall see later what the implications are for equilibrium constants. 

The initial compositions of both the infiltrating water and the solid materials may change due to their interaction, which in turn may affect the solubility and the pathway of dissolution-precipitation processes with time. When a particular component of the dissolved solution reaches a concentration greater than its solubility, a precipitation process occurs. Table 2.1 includes the solubility of selected sedimentary minerals in pure water at 25°C and total pressure of 1 bar, as well as their dissolution reactions. All of the minerals listed in Table 2.1 dissolve, so that the products of the mineral dissolution reactions are dissolved species. Figure 2.2 shows the example of gypsum precipitation with its increasing concentration in a NaCl aqueous solution. 

CN ions. Anodic dissolution of silver electrode in cyanide solutions and also the behavior of Ag at potentials preceding dissolution have been studied applying electrode impedance measurements [381]. At potentials of anodic dissolution, the process was represented by the equivalent circuit with two parallel branches. 

A 25-ml scintillation vial was charged with the step 1 product (7 g), tin(II)-2-ethyl-hexanoate, and ethylene glycol (7.507 mmol) and then thoroughly shaken using a KEM-Lab vortex mixer at 35 rpm. This mixture was then treated with 4,4 -methylene-bis(cyclohexylisocyanate) (11.262 mmol) and then further shaken by the vortex mixer for 1 minute. The vial was then placed into a heat shaker for 15 minutes and stirred to ensure its consistency and then returned to the heat shaker for 3.45 hours. Half of the hot mixture was removed from the vial and placed into a second vial, which was treated with 15 ml of /V, V-d i met h I ace tam i de and put onto the shaker until the biodegradable elastomer was dissolved. This solution was then precipitated in 1000 ml of water, the dissolution/precipitation process being repeated twice. Thereafter the precipitated polymer was isolated and purified by lyophilization. 

George R. Hill In the low temperature physical solution process the surface area would probably be that determined by BET adsorption measurements. In the high temperature process, apparently the coal structure is opened up, and the surface would be the total surface of all the molecular units. This occurs, as the dissolution proceeds, by a combination of chemical bond breaking and solvent action with hydrogen transfer to the free radicals produced. 

Dr. Hill In the low temperature solution process the activation energy value suggests that a physical process—probably diffusion—is rate controlling. The large (and increasing) value of the heat of activation for the major portion of the dissolution reaction requires that the rate is a chemically controlled process—very likely the breaking of chemical bonds. 

A number of attempts have been made to understand the mechanism of the adsorption of chelates on oxide minerals. For instance, IR spectroscopic studies10 have indicated the presence of a basic monosalicylaldoximate copper complex as well as the bis-salicylaldoximate complex on the surface of malachite (basic copper carbonate) treated with salicylaldoxime. However, other workers4 have shown that the copper chelate is partitioned between the surface and dispersed within the solution, and that a dissolution-precipitation process is responsible for the formation of the chelate. Research into the chemistry of the interaction of chelating collectors with mineral surfaces is still in its infancy, and it can be expected that future developments will depend on a better understanding of the surface coordination chemistry involved. 

For a solution-processed active interface, in which either the gate dielectric material is deposited from solution on to a solution-processible semiconducting material or vice versa, it is critical to avoid dissolution or swelling effects during deposition of the upper layer, which can lead to interfacial mixing and increased interface roughness. The preferred approach to achieve this is to choose orthogonal solvents for the deposition of the multilayer structure [23]. 

Electrochemical deposition of lithium usually forms a fresh Li surface which is exposed to the solution phase. The newly formed surface reacts immediately with the solution species and thus becomes covered by surface films composed of reduction products of solution species. In any event, the surface films that cover these electrodes have a multilayer structure [49], resulting from a delicate balance among several types of possible reduction processes of solution species, dissolution-deposition cycles of surface species, and secondary reactions between surface species and solution components, as explained above. Consequently, the microscopic surface film structure may be mosaiclike, containing different regions of surface species. The structure and composition of these surface films determine the morphology of Li dissolution-deposition processes and, thus, the performance of Li electrodes as battery anodes. Due to the mosaic structure of the surface... 

The problem of recovering the plutonium contained in the Pu/Al target dissolution solutions is trivial in comparison with the difficulties discussed above. The strong affinity exhibited by tertiary amine nitrates (TLA or T0A) for Pu(IV) was exploited to develop the following processes ... 

The weathering of minerals can be understood as a continuous dissolution-precipitation process involving them. The process can be very complicated, leading to multiphase equilibria, in which more than one solid phase, solution, and gas phase may be present. For example, primary silicates transform to secondary silicate minerals via such weathering reactions (Stumm and Wollast, 1990), as in the formation of kaolinite (AljSijC OH) from anorthite (CaAl2Si208) ... 

A number of experimental and theoretical studies of mass transfer in solution processes have been published. Since this literature is fairly well known, it will be mentioned briefly, but not analyzed in detail. Most of the earlier work in agitation employed dissolution rates as performance criteria (H6, H8, W5). Experimental studies of dissolution itself have employed suspended solute plates (B7, Wl), single crystals (M12, P5), revolving crystals (D2), and packed beds (Gl, L3, M5, V4). Recently, several theoretical analyses of literature data have appeared (El, HI, R3). A number of Russian investigators have also studied dissolution (N6, Zl) they prefer to correlate data in terms of individual variables rather than the dimensionless groups customary in English and American literature. 

H. J. ENGELL (Max Planck Institute) As already explained by Prof. Hackerman, two limiting mechanisms can be expected for the dissolution of a solid (a) Equilibrium exists at the phase boundary of the solid and the solution, and the transport of the dissolved solid into the interior of the solution is rate determining, (b) The rate determining step of the solution process is the transport through the phase boundary solid-solution then the transport of dissolved particles from the inter phase into the solution can be assumed to be fast enough to be without influence on the overall rate of the dissolution. 

Hydrothermal routes Under ambient conditions, the low reaction temperature and fast precipitation rate have deleterious effect on the crystallization and optical performance of rare earth vanadate nanomaterials. Referring to traditional solid-state reactions, bulk YV04 Eu phosphors require a calcinations temperature above 1300 K, but it is too high for the preparation of nanomaterials. Alternatively, hydrothermal routes could provide the adequate energy for solution phase reactions, which have been widely described in preparation of ceramic powders. The high pressure and temperature largely promote the dissolution-reprecipitation process, so as to decrease the lattice defects of NCs. With fine modulation, this method is also efficient to produce nano-sized crystals. 

Guyton s comprehensive vision for theoretical chemistry consisted of a dissolution model of chemical action. He added the Newtonian component of attraction to Louis Lemery s mechanistic model of solution process, drawing on a host of chemical authors Macquer, Boerhaave, Hoffman, Spielmann, Cadet, Boyle, Friend, Keill, Barchusen, Lemery, Bohn, Le Sage, and Limbourg. He also accepted Buffon s premise that chemical affinity or attraction depended on the shape and the relative position of particles, and that it followed the inverse square law ... 

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