Dissolution products

The safety sensor, however, gives only qualitative information. For a quantitative determination of the concentration of HF in a solution, it is necessary to determine JpS, which can be done by scanning the anodic potential from about 3 V to 0 V and measuring the relative current maximum in a unstirred solution. If JPS and the temperature T are determined, the electrolyte concentration c can be calculated using Eq. (4.9). This method of determining the concentration of HF is superior to simple measurements of the conductivity of the solution, because it is insensitive to dissolution products of Si or Si02, or to other ionic species in the analyte. 

It is therefore believed that at pH 6 and greater the corrosion process is localised and large local concentrations of ferrous iron are achieved. At pH 6 the oxidation to ferric iron is very rapid ( ) and precipitation of Fe(0H)j occurs to exhibit localised corrosion or "flash-rust" spots. At pH 5 and below a small but finite uniform dissolution of the iron substrate occurs. However, in this pH range the oxidation of the ferrous dissolution product to ferric ion is considerably slower, by almost 1000 times, and hence "flash rusting" is not observed. 

Suppressed retrogression of primary coal dissolution products resulting in enhanced distillate yield and residuum product quality... 

As an alternative to laboratory solubility measurements, solubility product constants (KSp), which are derived from thermodynamic data, can be used to calculate the solubility of solids in water (Table 2.9). Each solubility product constant describes a disassociation of a solid in water and calculates the activities or concentrations of the dissolution products in the saturated solution. The solubility product constant or another equilibrium constant of a reaction may be derived from the Gibbs free energy of the reaction (AG"K) as shown in the following equation ... 

In very acidic solutions (pH < 2.4-3) with ionic strengths below 0.1 M and at 25 °C and 1 bar pressure, scorodite has a pK of about 25.83 0.07. The pK of amorphous Fe(III) arsenate is approximately 23.0 0.3 under the same conditions (Langmuir, Mahoney and Rowson, 2006). At higher pH values, scorodite dissolves incongruently, which means that at least one of its dissolution products precipitates as a solid. The incongruent dissolution of scorodite in water leads to the formation of Fe(III) (oxy)(hydr)oxide precipitates that is, Le(III) (hydrous) oxides, (hydrous) hydroxides and (hydrous) oxyhydroxides (Chapter 3). During the formation and precipitation of the iron(III) (oxy)(hydr)oxides, As(V) probably coprecipitates with them (Chapter 3 also see Section 2.7.6.3). The dissolution rate of scorodite at 22 °C in pH 2-6 water is slow, around 10—9 —10—10 mol m-2 s-1, which explains its presence in many mining wastes (Harvey et al., 2006). 

Fig. 12.12. Example of potential-pH diagram for a system with a solid phase as a dissolution product. Iron has a tendency to corrode at all pHs, but at pH > 9 it forms Fe(OH)2.

Wise JP, Steams DM, Wetterhaun KE, et al. 1994. Cell-enhanced dissolution of carcinogenic lead chromate particles The role of individual dissolution products in clastogenesis. Carcinogenesis 15(10) 2249-2254. 

The mechanical properties of polyelectrolyte multilayer capsules have been subject of several studies using different methods. Baumler and co-workers [7] have used the micropipette technique and found that PMCs are not conserving their volume if pressure differences are applied between inside and outside of the shell. This is expected, since the shells can only be formed in first place because the membrane is permeable to low molecular weight species, the core dissolution products. They found no deformation up to a critical pressure followed by an irreversible collapse, showing that shells deform not elastically but plastically for large deformations. First quantitative estimates of the Young s modulus of the shell material were obtained by Gao and coworkers, using osmotic pressure differences between inside and outside of the shell [8,9], These authors monitored the onset of the buck-... 

Congruent dissolution refers to the potential of a mineral to undergo dissolution but not form any secondary minerals by the dissolution products. For example, in the... 

Volatile1) compounds All (1) C6H6/CH3OH extraction (2) CH2CI2 extraction of HC1, HF dissolution products GLC.GC—MS HRMS... 

Formation of a ceramic with magnetite is possible because it is sparsely soluble. This may be seen by calculating the pi sp of magnetite using its Gibbs free energies and that of dissolution products (listed in Appendix B), and the aqueous solubility equation... 

This layer contains a larger amount of dissolution products than the bulk of the electrolyte. When the polishing current is turned off after the two electrodes are short-circuited, the viscous layer is gradually eliminated by diffusion and the polarization current progressively decreases. Fig. 3 shows die varia -tion of the current density with time for different size anodes... 

Finally, X reacts to form the dissolution product SiFs" through a sequence of chemical steps involving HF and coupled with hydrogen evolution. 

Some dissolution products adsorb onto the abrasive particle and are moved away from the surface ... 

Soluble mucus was considered to be the transient physical dissolution product of the visible surface mucin before it undergoes further enzymatic degradation in the stomach (Gll). It precipitates from filter ... 

Figure 13.5. Transport vs surface controlled dissolution. Schematic representation of concentration in solution, C, as a function of distance from the surface of the dissolving mineral. In the lower part of the figure, the change in concentration (e.g., in a batch dissolution experiment) is given as a function of time, (a) Transport controlled dissolution. The concentration immediately adjacent to the mineral reflects the solubility equilibrium. Dissolution is then limited by the rate at which dissolved dissolution products are transported (diffusion, advection) to the bulk of the solution. Faster dissolution results from increased flow velocities or increased stirring. The supply of a reactant to the surface may also control the dissolution rate, (b) Pure surface controlled dissolution results when detachment from the mineral surface via surface reactions is so slow that concentrations adjacent to the surface build up to values essentially the same as in the surrounding bulk solution. Dissolution is not affected by increased flow velocities or stirring. A situation, intermediate between (a) and (b)—a mixed transport-surface reaction controlled kinetics—may develop.

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