Static solubility

Figure 16. High-pressure optical cell for static solubility measurements (1 = soft-iron wire, 2 = Bridgman piston, 3 = screw cap, 4 = thrust collar, 5 = teflon packing, 6 = inner Bridgman piston, 7 = cap of autoclave, 8 = sliding piston, 9 = body of autoclave, 10 = window fitting, 11 = sapphire window, 12 = sample container, 13 = sealing screw, 14 = stirring rod for details see [45,76]).

Solubility. Sohd—Hquid equihbrium, or the solubiHty of a chemical compound in a solvent, refers to the amount of solute that can be dissolved at constant temperature, pressure, and system composition in other words, the maximum concentration of the solute in the solvent at static conditions. In a system consisting of a solute and a solvent, specifying system temperature and pressure fixes ah. other intensive variables. In particular, the composition of each of the two phases is fixed, and solubiHty diagrams of the type shown for a hypothetical mixture of R and S in Figure 2 can be constmcted. Such a system is said to form an eutectic, ie, there is a condition at which both R and S crystallize into a soHd phase at a fixed ratio that is identical to their ratio in solution. Consequently, there is no change in the composition of residual Hquor as a result of crystallization. 

The invasion of particles can be eliminated either by using solids-free systems or by formation of a competent filter cake on the rock surface. If the components forming the filter cake are correctly chosen and blended, they will form a very effective downhole filter element. This ensures that colloidal sized clays or polymeric materials are retained within the filter cake and do not enter the formation. Further protection is provided by ensuring that a thin filter cake is formed due to low dynamic and static filtrate losses. Thus, the cake may be easily removed when the well is brought into production. Additionally, the filter cake can be soluble in acid or oil. 

In general, it is fair to state that one of the major difficulties in interpreting, and consequently in establishing definitive tests of, corrosion phenomena in fused metal or salt environments is the large influence of very small, and therefore not easily controlled, variations in solubility, impurity concentration, temperature gradient, etc. . For example, the solubility of iron in liquid mercury is of the order of 5 x 10 at 649°C, and static tests show iron and steel to be practically unaltered by exposure to mercury. Nevertheless, in mercury boiler service, severe operating difficulties were encountered owing to the mass transfer of iron from the hot to the cold portions of the unit. Another minute variation was found substantially to alleviate the problem the presence of 10 ppm of titanium in the mercury reduced the rate of attack to an inappreciable value at 650°C as little as 1 ppm of titanium was similarly effective at 454°C . 

Static test results may be evaluated by measurement of change of mass or section thickness, but metallographic and X-ray examination to determine the nature and extent of attack are of greater value because difficulty can be encountered in removing adherent layers of solidified corrodent from the surface of the specimen on completion of the exposure, particularly where irregular attack has occurred. Changes in the corrodent, ascertained by chemical analysis, are often of considerable value also. In view of the low solubility of many construction materials in liquid metals and salts, changes in mass or section thickness should be evaluated cautiously. A limited volume of liquid metal could become saturated early in the test and the reaction would thus be stifled when only a small corrosion loss... 

Supercritical fluid extraction can be performed in a static system with the attainment of a steady-state equilibrium or in a continuous leaching mode (dynamic mode) for which equilibrium is unlikely to be obtained (257,260). In most instances the dynamic approach has been preferred, although the selection of the method probably depends just as much on the properties of the matrix as those of the analyte. The potential for saturation of a component with limited solubility in a static solvent pool may hinder complete recovery of the analyte. In a dynamic system, the analyte is continuously exposed to a fresh stream of solvent, increasing the rate of extraction from the matrix. In a static systea... 

SFE can be carried out in three different ways. In a static extraction (no flow-rate), the extraction vessel is pressurised to the desired pressure with the extracting fluid and then simply left for a certain length of time. The main benefit of this method is that the fluid has time to penetrate the matrix. It is most applicable when the analyte has a high affinity for the solvent and a low affinity for the matrix and also when the solubility limit of the analyte in the fluid is much higher than the actual level reached during the extraction [89]. This method was popular in early SFE experiments but has declined in favour of dynamic SFE. Here, fresh SCF is continuously passed over the sample, extracting soluble compounds and depositing them in a suitable solvent or on a solid trap. The dynamic mode is particularly useful when the concentration of the solute... 

The ability of SFE-FTIR to perform a variety of extraction methods is a definite advantage, especially for the study of complex mixtures containing analytes of varying solubility. For analytes which are readily solubilised in C02, direct dynamic and direct static-dynamic SFE-FTIR methods are quite successful. Elimination of the trapping process reduces both analysis time and potential analyte loss arising from... 

Static pressure Total applied pressure Gas solubility Intensity of collapse Bubble content... 

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