Volume diffusion INDEX

Rate-determining mechanism depends also on saturation index and pH. Rate-determining step for precipitation of salt minerals such as BaS04 from supersaturated aqueous solution is volume diffusion in aqueous solution, but surface reaction controls the precipitation when degree of supersaturation is small (Nielsen 1958). 

A further benefit of the low absorbtivity of most samples in the NIR is that measurements involving scattering effects (both diffuse transmission and diffuse reflectance) are possible. The penetration depth of the sampling beam in diffuse reflectance measurements of powders in the NIR can be on the scale of millimeters, despite the numerous refractive index interfaces and extended optical path involved. Thus relatively large volumes of material can be interrogated, avoiding problems of surface contamination and sample nonhomogeneity. 

The emission index in general is defined as the mass of pollutant emitted per unit mass of fuel consumed. In quasi-steady diffusion flames, this is the ratio of the mass flux of pollutant out of the flame to the mass rate of consumption of fuel per unit flame area. Depending on the application, it may be more desirable to consider only the flux of pollutant to the air or the sum of the pollutant flux to both air and fuel. The latter definition is selected here, and a pollutant balance for the flame then enables the emission index to be expressed as the ratio of the mass rate of production of pollutant per unit area to the mass rate of consumption of fuel per unit area. In terms of the mass rate of production of species i per unit volume cDj, the mixture fraction, and the magnitude of its gradient VZ, the mass rate of production of species i per unit area is... 

Radioactive label, 330 Raman diffusion, 184 Raman scattering, 227 Ratio fluorimeter, 228 Rayleigh scattering, 226 Real mean, 385 Red-shift, 196 Reference electrode, 347 Reflectron, 298 Refractive index detector, 59 Relative response factor, 78 Relative standard deviation, 387 Reliability, 389 Resolving power, 282 Response factor, 77 Restrictor, 98 Retardation factor, 88 Retention factor, 14 Retention index, 41 Retention time, 7 Retention volume, 14 RP-18, 53 RSD, 387 Ruhemann, 112... 

The proper choice of a solvent for a particular application depends on several factors, among which its physical properties are of prime importance. The solvent should first of all be liquid under the temperature and pressure conditions at which it is employed. Its thermodynamic properties, such as the density and vapour pressure, and their temperature and pressure coefficients, as well as the heat capacity and surface tension, and transport properties, such as viscosity, diffusion coefficient, and thermal conductivity also need to be considered. Electrical, optical and magnetic properties, such as the dipole moment, dielectric constant, refractive index, magnetic susceptibility, and electrical conductance are relevant too. Furthermore, molecular characteristics, such as the size, surface area and volume, as well as orientational relaxation times have appreciable bearing on the applicability of a solvent or on the interpretation of solvent effects. These properties are discussed and presented in this Chapter. 

In the diffusive interfacial transport-refractive index (DIT-NDX) method, compositions are determined using precise refractive index data (8). Refractive index data valid to +/- 0.00005 are obtainable using the DIT apparatus vithin an area of 30 ym2 in a sample approximately 25-ym thick (0.75 picoliter volume). Data collection and analysis require 9 seconds. The accuracy, spatial resolution, and speed vith vhich refractive indices can be determined are thus superb. 

The free-volume-filling responses are linear and all produce a positive change in refractive index or a negative change in phase. The anal3des diffuse into the void volume in the Teflon AF and do so reversibly, as shown in the time plot in Fig. 18, where a step function in concentration of various aromatics is introduced to the Teflon AF -coated interferometer. Benzene, toluene, and xylene diffuse into the Teflon AF from a solution containing known concentrations of the aromatic... 

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