Stability 486 INDEX

Calcium—In general, calcium (as CaCOs) below 800 ppm should not result in calcium sulfate scale. In arid climates, however, the critical level may be much lower. For calcium carbonate scaling tendencies, calculate the Langelier Saturation Index or the Ryznar Stability Index. 

Sufficient stability of the hydrocarbon ions, as the salt or in the solution, is an obvious prerequisite for these procedures, and, in practice, selecting or designing the stable ions and choosing a proper solvent are tasks of primary importance. As an ordinary stability index for the ions, thermodynamic scales referred to the water molecule, i.e. p CR+ and pKa values, are chosen for the carbocation and carbanion, respectively. 

As thermodynamic stability indexes for the hydrocarbon ions, pA R+ and pA a values [(4) and (5)] have been widely applied for the carbocation and carbanion, respectively, in solution. Here K + stands for the equilibrium constant for the reaction (6) of a carbocation and a water molecule stands for the equilibrium constant for the reaction (7) of a hydrocarbon with a water molecule to give the conjugate carbanion. The equilibrium constants are given by (8) and (9) for dilute aqueous solutions. Obviously, the reference system for the pKn+ scale is the corresponding alcohol, and... 

A method to estimate the optimal dose of a scale inhibitor has been described [1223]. The method starts with noting the chemical composition and temperature of the water. From these parameters a stability index is calculated, allowing for the prediction of the optimal dose of a scale inhibitor. 

There have been several comments and criticisms of this sequence.51,52,57 Buchler51,52 has suggested a stability index, 5 ... 

Table 2 Buchler s stability index 5 and stability classes for metallo-octaalkylporphyrins.

Fig. 4.7 Plot of the log of the relative rates of hydrolysis of MP and the corresponding Ni(II)P vs. the stability index S . The parameter Sj is defined as 100 lE /r- where z = charge,...

The ideas of equality of carbon-carbon bond lengths as a characteristic attribute of a stable aromatic molecule (61JCS859 64PAC363) were embodied in the form of the aromatic stability index of Julg (76TCA249). 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

Sadana and collaborators (Sadana, Raju and Shahin, 1989) have proposed an empirical stability index (SI) for enzyme deactivation, which makes more quantitative the effect of different variables on enzyme stability. 

Sadana, A., Raju, R.R. and Shahin, E. (1989) A stability index for enzyme deactivation. 

SiMouO ]4-.134 The structure of the heteropoly blue species (four-electron-reduced PM012O40]3-) formed in the molybdenum blue determination of phosphorus has been reported135 and a review of molybdate heteropoly blues has appeared.130 A stability index of polyanion structures has been discussed.137 The presence of two PMo, anions in aqueous solutions of molybdate and phosphate has been demonstrated by 31P NMR.138 Solid state NMR (nonspinning and MAS techniques) has been used for characterization of heteropolyanions.139 Molybdenum-95 NMR spectra of some polymolybdates have been reported.140... 

Calculations based on Stiff and Davies stability index (Ref. 11 indicated that under normal producing temperatures formation water 1s not expected to form scale. However, the high skin temperature (up to 150° C) of the crude heaters will cause severe CaCO-scaling. This expectation was confirmed by laboratory tests using synthetic formation water. The result indicates a requirement to Inject scale inhibitor upstream of the heaters. A polyphosphate scale inhibitor was found to be effective in the laboratory tests. 

The stability of a metalloporphyrin can be roughly estimated by the charge-to-radius ratio (Z/yj). Buchler et al 1 found that the stability index, SI = 100(ZAr/yj), where X is the Pauling electronegativity, predicts the stability of a metalloporphyrin to acid demetallation, and correlated the SI to the Falk-Phillips stability criteria (Table 2). 

A sample is heated, usually at or above 100°C, while air is bubbled through it, and the volatiles created are transferred to a water trap where conductivity is measured (Fig. D2.3.1). The induction period endpoint is determined by the time it takes for the sample to begin a rapid increase in conductivity. The time required for the sample to reach its induction period endpoint is termed the Oil Stability Index (OSI). The Oil Stability Index is Official Method Cd 12b-92 of the American Oil Chemists Society (AOCS, 1996). 

Figure D2.3.1 Schematic diagram of oil stability index (OSI) instrumentation.

Figure D2.3.2 Data from conductivity probe and determination of oil stability index (OSI) by Lipid Oxidation/ drawing tangents. Stability...

The oil stability index (OSI) method provides results in a matter of hours instead of months (required for studies done at ambient temperatures). These OSI results are useful as comparative measures of oxidative stability, i.e., to determine the effect of a treatment or antioxidant compared to a control sample. Meaningful predictions of the actual shelf lives of specific commodities require that such shelf life studies be performed at ambient conditions. If only accelerated tests are to be performed, two or more tests based on different principles of lipid oxidation measurement should be conducted the effect of accelerated storage temperature should also be investigated. 

Food deterioration desiccation/water activity, 61 -66 oil stability index, 541-545 primary lipid oxidation products,... 

Rancidity in food, measurement of oil stability index, 541 -545 secondary lipid oxidation, 531-539 Rapeseed oil, properties and composition of, 474 (table)... 

LANGELIER AND RYZNAR EQUATIONS SATURATION AND STABILITY INDEX... 

If the Stability Index ranges from 6.5 to 7.0, the water is in a good range. 

When the number of concentrations of the circulating water is in the order of 3-7, some of the salts dissolved can exceed their solubility limits and precipitate, causing scale formation in pipes and coolers. The purpose of the treatment of the cooling water is to avoid scale formation. This is achieved by the injection of sulfuric acid to convert Ca and Mg carbonates (carbonate hardness) into more soluble sulfates. The amount of acid used must be limited to maintain some residual alkalinity in the system. If the system pH is reduced to far below 7.0, it would result in an accelerated corrosion within the system. As stated earlier, scale formation and/or corrosion tendency is defined by the Saturation Index (Langelier Index) and Stability Index (Ryznar equation). 

If the Saturation Index is positive (which implies that the Stability Index is less than 6.5), then the water has scale tendency and the addition of sulfuric acid in appropriate quantities would be required to prevent scaling formation. The following example illustrates the estimation of the required amount of acid. 

Over the years, the use and application of several different saturation indices that aid the prediction of scaling and corrosion potential in different waters have evolved to become an integral part of the business of treating and managing cooling water systems. The two most popular are the Lange-lier Saturation Index (LSI) and the Ryznar Stability Index (SI), which were both introduced more than 50 years ago. 

The most widely known of these alternative indices is probably the Ryznar Stability Index (Ryznar Index, Stability Index) (SI), which is a direct derivation of LSI and is based on observed field data. It is generally considered more useful than the LSI in water systems flowing at or above 2 ft/sec (0.6 m/sec), such as occurs in most cooling systems. 

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