Size fractionation experimental method

Experimental Results—Gottschalk and Wartman (loc cit) investigated the properties of a number of magnetite powders. Magnetites from four sources were purified and sized, each size-fraction then being analyzed for FesC>4. Only size-fractions below 100-U. S. mesh were studied. Sizes below 350-mesh were air elutriated by the Roller method. 

It should be emphasized here that experimental data about bandedge shifts or the complete spectra can only be obtained with colloidal solutions which have a sufficiently narrow size distribution. Monodispersive samples were obtained by selecting a proper synthesis method (see e.g. refs. [22, 23]) or by size fractionations such as gel-electrophoresis and selective precipitation [87, 88]. One example is the absorption of InP colloids with different diameters [23] (Fig. 9.5). In many cases the particle sizes were determined by transmission electron microscopy (TEM). It should also be mentioned here that in most cases cluster growth occurs, i.e. the bigger particles grow at the expense of the smaller ones, which can easily be detected in the absorption spectrum. In order to avoid agglomeration, most semiconductor clusters were prepared in the... 

For periodic structures, the continuity equations may also be solved explicitly by multipole expansion to yield tractable series solutions [59,60], T o a first approximation, these treatments are equivalent at low volume fractions of solids. Experimental studies of diffusion of small nonadsorbing solutes within ordered assemblies of colloids is has been well predicted by these treatments [31,59,60]. However, these theories do not consider solutes of nonzero size, and another method is necessary to examine this. 

Also shown in Fig. III.3 is the dependence of the experimental accuracy on the nonuniformity of particle diameter in the dust fractions (curve 1). With Ad/d v = 0.05, the error of the method is 15%. Hence, the tilt-plate method will give accurate results only if the particles are monodisperse. If the particle size varies significantly within the fraction, the method is less accurate, becoming unsuitable in practice for the determination of particle adhesive force for example, with d = 40-60 /rm, we find that Adld y = 0.2 and B = 60%. 

Size-exclusion chromatography fractionation is steric, that is, dimensional. In theory, a SEC system could be calibrated by means of some appropriate standards of known dimensions and, in this way, to measure SEC fractionation depends on the hydrodynamic radius Rh of the macromolecules Rh M[r]] where [17] is the intrinsic viscosity. sY and Rh are two different parameters. I Y is an equilibrium parameter Rif isa dynamic parameter and depends on the method by which it is obtained. Rh becomes the Stokes radius R in diffusion measurements and the Einstein radius R in viscosity measurements. Because SEC fractionation depends on Rh, the method is not appropriate for a direct measure of YY- Convenient experimental methods to measure sY are scattering techniques. 

The particles were separated into fractions by a sifting method [34]. Later [21], spherical glass particles less than 100 m in diameter were studied after preliminary separation into constant-size fractions by an air-fractioning procedure. Steel surfaces of the 9th class of surface finish were given continuous powder layers over an area of 3 cm (all the experimental data were referred to 1 cm of the test surface). 

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