Extraneous Effects

The bimodal pore distribution model used by Gibilaro et aL may also be used to analyze the results of this type of experiment. If it is assumed that all extraneous effects due to mixing in the interstices between the pellets have been eliminated by means of a control experiment, the results corresponding to equations (10.39) and (10.40) are now... 

Aeration of Solution Unless specified, the solution should not be aerated. Most tests related to process equipment should be run with the natural atmosphere inherent in the process, such as the vapors of the boiling liquid. If aeration is used, the specimens should not be located in the direc t air stream from the sparger. Extraneous effects can be encountered if the air stream impinges on the specimens. 

The Nernst equation is of limited use at low absolute concentrations of the ions. At concentrations of 10 to 10 mol/L and the customary ratios between electrode surface area and electrolyte volume (SIV 10 cm ), the number of ions present in the electric double layer is comparable with that in the bulk electrolyte. Hence, EDL formation is associated with a change in bulk concentration, and the potential will no longer be the equilibrium potential with respect to the original concentration. Moreover, at these concentrations the exchange current densities are greatly reduced, and the potential is readily altered under the influence of extraneous effects. An absolute concentration of the potential-determining substances of 10 to 10 mol/L can be regarded as the limit of application of the Nernst equation. Such a limitation does not exist for low-equilibrium concentrations. 

Certain types of corrosion are selective. Thus, corrosion cracking is observed primarily in the case of alloys and only when these are in contact with particular media. Corrosion is often enhanced by various extraneous effects. Stress corrosion cracking can occur under appreciable mechanical loads or internal stresses corrosion fatigue develops under prolonged cyclic mechanical loads (i.e., loads alternating in sign). 

But here is what Philip Brown did He took a different tack on the question. He set up and performed an experiment wherein he took different sugars (fructose, glucose, and sucrose) and made up solutions by dissolving them in water, each at five different concentration levels, and made solutions using all combinations of concentrations. That gave an experimental design with 125 samples. He then measured the spectra of all of those samples. Since the samples were all clear solutions there were no extraneous effects due to optical scatter. 

TABLE 5.7 CHANGES TO DETECTOR OUTPUT DUE TO EXTRANEOUS EFFECTS... 

The data for assessing the role of formaldehyde in the oxidation of hydrocarbons below 400° C. are summarized in Table IV. It is evident that generalizations at this time are premature, and it is difficult to determine whether the difference reported for the various hydrocarbons are indeed characteristic of the individual species, or that such extraneous effects as variation in surface conditions, sampling techniques, precision of analytical methods, or reactions between end products such as peroxides and aldehydes are significant. 

Alternatively one can in principle derive both micropore and macropore diffusivities from measurements of the transient uptake rate for a particle (or assemblage of crystals) subjected to a step change in ambient sorbate pressure or concentration. The main problem with this approach is that the overall uptake rate may be controlled by several different processes, including both heat and extraparticle mass transfer as well as intraparticle or intracrystalline diffusion. The intrusion of such rate processes is not always obvious from a cursory examination of the experimental data, and the literature of the subject is replete with incorrect diffusivities (usually erroneously low values) obtained as a result of intrusion of such extraneous effects. Nevertheless, provided that intraparticle diffusion is sufficiently slow, the method offers a useful practical alternative to the Wicke-Kallen bach method. 

Before actual data can be fit to a model, extraneous effects manifested in the trace must be removed, such as the shift in baseline as a result of the change in heat capacity of the sample during the transformation (see section 3.7.2). It may, for some device designs (e.g. post-type DTA), be difficult to purify the instrument output to represent only the latent heat from the transformation because of random baseline float. Hence, the data set fitting a particular model is a necessary but insufficient criterion for guaranteeing that the model describes the measured phenomenon. 

Introduction. The use of electrical measurements has been fairly important in the study of H bond association. In the main, this is the result of three facts (1) the experimental quantities are readily obtained (2) dipole moments calculated from the measured quantities have directionally additive properties and therefore can often allow a choice between various possible structures (3) dielectric dispersion studies permit separation of the several kinds of rearrangements that occur. The experimental determinations have increased in complexity as more extensive ranges of frequency are scanned in studying dielectric dispersion, as biological and polymeric substances become of interest, and as improved theories demand more accurate data. The advantage of the directional aspects of the dipole vector is somewhat nullified by extraneous effects of the solvent and of parts of the molecule not involved in H bonding. 

Figure 4 compares several of these models with respect to the nature of the constants that each uses. The simplest model (linear sorption or Ai ) is the most empirical model and is widely used in contaminant transport models. values are relatively easy to obtain using the batch methods described above. The Aid model requires a single distribution constant, but the Aid value is conditional with respect to a large number of variables. Thus, even if a batch Aid experiment is carefully carried out to avoid introduction of extraneous effects such as precipitation, the Aid value that is obtained is valid only for the particular conditions of the experiment. As Figure 4 shows, the radionuclide concentration, pH, major and minor element composition, rock mineralogy, particle size and solid-surface-area/solution volume ratio must be specified for each Aid value. 

Relaxation rates of nuclear spins can also be related to aspects of molecular structure and behaviour in favourable circumstances, in particular internal molecular motions. It is true to say, however, that the relationship between relaxation rates and structural features are not as well defined as those of the chemical shift and spin-spin coupling constants, and are not used on a routine basis. The problem of reliable interpretation of relaxation data arises largely from the numerous extraneous effects that influence experimental results, meaning empirical correlations for using such data are not generally available and this aspect of NMR will not be pursued further in this book. 

The problem of measuring the emf produced by centrifugal action was first successfully solved by Tolman (loc at) The success depended essentially upon the mechanical arrangements whereby very high rotation frequency could be realised without undue introduction of extraneous effects which would influence the observations For the details of the expenmental arrangement the original paper must be consulted. It is proposed only to summarise here the results... 

There is much more work to be done before the model can make quantitative predictions of all of these effects, but in its present form, the bond valence model does provide a means of understanding the structure and predicting the geometry that would be expected in the absence of extraneous effects. This can then be used to examine the relative importance of different types of strain, leading to a better appreciation of the roles of, and interconnections between, the different influences at work in inorganic solids. 

Reaction rates can be controlled by the rate of conversion of the reactants or by nonchemical rate processes such as the rate of diflusion of reactants or the rate of heat transfer. In the study of chemical kinetics we will be interested in the rates of chemical change governed by the speed of chemical processes. Any investigation of reaction rates meant for mechanistic studies must first establish that this is what we are measuring. Fortunately, it is relatively easy to check for extraneous effects before the kinetic investigation is undertaken. The effects that are most likely to cause problems involve diffusion of mass and heat in catalyst particles and mixing in the reactor. 

Attempts have been made to devise calculation al methods of testing for the influence of diffusion on the observed rates of reaction. These non-experimental methods for identifying non-chemical influences on reaction rates are highly constrained in their applicability, for example to first order reactions, and often require estimates of hard-to-estimate quantities such as diffusivities. At best these procedures salve one s conscience more often, they are prone to mislead. The reasons for this are that the mathematics required to estimate the influence of intervening rates are very difficult and only the simplest of cases lead to predictive analytical formulas. In general the only reliable examination of the influence of extraneous effects on the observed rate of reaction consists of an appropriate experimental test. 

Both types of diffusion studies require numerous difficult experiments in conventional reactors, and as a result they are rarely carried out. However, lacking the assurance that the kinetic data is free of extraneous effects, we cannot be sure that it can be reproduced in any other reactor. 

The Lambert Beer equation is always considered to be obeyed exactly. However, apparent deviations are sometimes observed, and it is then necessary to find an explanation in terms of extraneous effects such as dissociation and complex formation. Thus, when certain substances are present in solution, there are shifts in equilibria, and consequent changes in the relative proportions of the various molecular components. If the absorption of light by one of these components is being observed, there will be an apparent deviation from Beer s law, equation (2,16). Also, solutions that scatter light will not obey the law, and it is therefore important to exclude dust particles and large aggregated molecules in photometric experiments. 

This mode of deformation has been known for a long time and the experimental evidence prior to 1958 has been reviewed by Glen (1958). Experiments on single crystals are obviously of great help because there must be many extraneous effects in polycrystal-... 

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