Average Relative Particle Masses

Data describing the average size of the molecule, such as the average relative particle mass M and the carbon number ZC, may be correlated satisfactorily with data from thermoanalysis, which describes the evaporation behavior, such as the start temperatures of evaporation, Tl % and T5 %, and the distillable fraction of the sample, AG400. Surprisingly and without logical explanation, the residue / 800 can also be correlated. 

Bitumens are colloid systems, as are crude oils, and consist of the two colloidal components, petroleum resins and asphaltenes, dispersed in a dispersion medium. To investigate the composition of the system, a colloid precipitation according to Neumann [4-10] is carried out. The chemical nature of the bitumen and its components were determined by element analysis, where the atomic ratio H/C includes an indicator of the aromacity. Further characterization is performed by measuring the average relative particle mass (mean of the molecular weight M) by vapor pressure osmometry. 

The elemental composition and the average relative particle mass of the bitumens and their separated colloid components were determined (Tables 4-49 - 4-52)... 

Table 4-49 Element analysis (wt %) and average relative particle mass of the bitumen.

The influence of the concentration of the dispersion medium or the maltenes and their average relative particle mass M is seen. If we define this influence using factors ... 

In contrast to osmotic pressure, light-scattering measurements become easier as the particle size increases. For spherical particles the upper limit of applicability of the Debye equation is a particle diameter of c. A/20 (i.e. 20-25 nm for A0 600 nm or Awater 450 nm or a relative molecular mass of the order of 10 ). For asymmetric particles this upper limit is lower. However, by modification of the theory, much larger particles can also be studied by light scattering methods. For polydispersed systems a mass-average relative molecular mass is given. 

Colloidal systems are generally of a polydispersed nature - i.e. the molecules or particles in a particular sample vary in size. By virtue of their stepwise build-up, colloidal particle and polymer molecular sizes tend to have skew distributions, as illustrated in Figure 1.2, for which the Poisson distribution often offers a good approximation. Very often, detailed determination of relative molecular mass or particle size distribution is impracticable and less perfect experimental methods, which yield average values, must be accepted. The significance of the word average depends on the relative contributions of the various molecules or particles to the property of the system which is being measured. 

Table VI summarizes aerosol mass concentrations and composition in different regions of the troposphere. It is interesting to note that average total fine particle mass (that associated with particles of diameter less than about 2 /im) in non-urban continental, i.e., regional, aerosols is only a factor of two lower than urban values. This reflects the relatively long residence time of particles (recall the estimate of a lifetime of fine particles by dry deposition of 10 days). Correspondingly, the average composition of non-urban continental and urban aerosols is roughly the same. The average mass concentration of remote aerosols is a factor of three lower than that of non-urban continental aerosols. The elemental carbon component, a direct indicator of anthropogenic combustion sources, drops to 0.3% in the remote aerosols, but sulfate is still a major compo-...

The concentration of atmospheric aerosols varies considerably in space and time. This variability of the aerosol concentration field is determined by meteorology and the emissions of aerosols and their precursors. For example, the annual average concentration of PM2.5 in North America varies by more than an order of magnitude as one moves from the clean remote to the polluted urban areas of Mexico City and southern California (Figure 8.24). Sulfate dominates the fine aerosol composition in the eastern United States, while organics are major contributors to the aerosol mass everywhere. Nitrates are major components of the PM2.5 in the western United States. The EC makes a relatively small contribution to the particle mass in many areas, but because of its ability to absorb light and its toxicity, it is an important component of atmospheric particulate matter. 

Hydrodynamic Sizes Relative to Airborne Sizes of Metal Oxide Particles Particles in dry form were found to be smaller than 1000 nm for fine zinc oxide dust and 50 to 70 nm for ultrafine zinc oxide dust (7). Particles were sonicated for 30 minutes. When suspended in distilled water, 20% of the ultrafine (nano) zinc oxide particles were suspended, with an average hydrodynamic diameter of 170 to 250 nm. When suspended in tissue culture media 45% had an average hydro-dynamic diameter of 300 to 400 nm. Tissue culture media suspended or extracted two to three times more particle mass than did dilute buffer or deionized distilled water, because of hydrodynamic action of media minerals. Hydrodynamic diameters were only modestly larger in tissue culture media than in distilled water (7). 

Avogadro s number has been experimentally determined by several methods. How does it relate to atomic mass units Remember that the atomic mass for an element is the average relative mass of all the isotopes for the element. The atomic mass (expressed in grams) of 1 mole of any element contains the same number of particles (Avogadro s number) as there are in exactly 12 g of C. Thus, 1 mole of anything is the amount of the substance that contains the same number of items as there are atoms in exactly 12 g of C. 

Detachment of Particles as a Function of Flow Velocity. A study was also made of the relation between 7p (the adhesion number) and the average water-flow velocity (Fig. VII.4). Naturally, with increasing water-flow velocity the mass of the adhering particles will fall more sharply than the number of particles, since it is easier to remove the larger particles, which carry relative greater masses. 

True Density or Specific Gravity. The average mass per unit volume of the individual particles is called the tme density or specific gravity. This property is most important when volume or mass of the filled composition is a key performance variable. The tme density of fillers composed of relatively large, nonporous, spherical particles is usually determined by a simple Hquid displacement method. Finely divided, porous, or irregular fillers should be measured using a gas pycnometer to assure that all pores, cracks, and crevices are penetrated. 

The proposed technique will be used here to illustrate the case of interfacial heat and multicomponent mass transfer in a perfectly mixed gas-liquid disperser. Since in this case the holding time is also the average residence time, the gas and liquid phases spend the same time on the average. If xc = zd = f, then for small values of t, the local residence times tc and td of adjacent elements of the continuous and dispersed phases are nearly of the same order of magnitude, and hence these two elements remain in the disperser for nearly equal times. One may conclude from this that the local relative velocity between them is negligibly small, at least for small average residence times. Gal-Or and Walatka (G9) have recently shown that this is justified especially in dispersions of high <6 values and relatively small bubbles in actual practice where surfactants are present. Under this domain, Eqs. (66), (68), (69) show that as the bubble size decreases, the quantity of surfactants necessary to make a bubble behave like a solid particle becomes smaller. Under these circumstances (pd + y) - oo and Eq. (69) reduces to... 

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