Particle-size distribution conclusions

In order to calculate particle size distributions in the adsorption regime and also to determine the relative effects of wavelength on the extinction cross section and imaginary refractive index of the particles, a series of turbidity meas irements were made on the polystyrene standards using a variable wavelength UV detector. More detailed discussions are presented elsewhere (23) > shown here is a brief summary of some of the major results and conclusions. 

Evaluation of the morphology of a pharmaceutical solid is of extreme importance, since this property exerts a significant influence over the bulk powder properties of the material. In addition to providing insights into the micromeritic properties of the solid, microscopy can also be used to develop preliminary estimations of the particle-size distribution. A determination can be easily made regarding the relative crystallinity of the material, and it is often possible to deduce crystallographic information as well. Unknown particulates can often be identified solely on the basis of their microscopic characteristics, although it is useful to obtain confirmatory support for these conclusions with the aid of microscopically assisted techniques. 

Science the authors of one paper (04) concluded that particle size is of no relevance in determining the flow behavior of suspensions, although the particle-size distribution is. The authors of the very next paper (Zl), on the other hand, documented the opposite conclusion. Until the reasons for such completely different types of behavior in apparently similar systems are understood, the role of the engineer is necessarily primarily one of evolving processes for fluids of predetermined behavior rather than one of questioning in detail how such behavior comes about or how it may be modified. 

Conclusions. Our theoretical and experimental work has shown conclusively that acoustic agglomeration does result in shifting the particle size distribution from submicrometer sizes into the 10 micrometers and above size range. In order to achieve the desired 150 to 160 dB, specific acoustic powers of from 0.1 to 1 watt/cm2 are required for plane wave propagation and less than that for standing wave chambers. 

From the particle size distributions shown in Fig. 13.2 combined with the shape information provided in the optical micrograph (Fig. 13.1), it is difficult to make any clear conclusions about the differences observed in the distributions. Because of the high aspect ratio of the material, the distributions are multimodal. Additionally, it cannot be stated that the differences in the distributions are due to size alone. It is quite probable that observable differences are created by variations in particle shape. 

In conclusion, the direct reduction is a fast process taking place between 150 and 200°C, resulting in relatively large particles with an average size of 14-16A and a bimodal particle size distribution. The desorption of NH3 and H2O at 211°C is caused by the decomposition of NH4NO3 in an independent process of the reduction. 

The overall conclusion from the analysis of equation 18 over the complete domain of a is that, in principle, information about the shape of the particle size distribution can be obtained directly from turbidity, or in general, from scattering measurements. However, the discriminating power of the measurements in terms of the particle size distribution depends upon the wavelength range selected for the analysis. The major difficulty in the interpretation of the data arises from the behavior of the extinction itself as function of the size parameter which causes the measurements "see" a different average at every wavelength. 

All the above formulas are one-parameter equations, i.e. they relate the dispersion viscosity only to the volume fraction of particles contained in it. This limits the range of applicability of the equations to not very high dispersion concentrations. To take account of the influence of the structure of concentrated dispersions on their rheological behavior, Robinson [12] suggested that the viscosity of dispersions is not only propertional to the volume fraction of solid phase, but is also inversely proportional to the fraction of voids in it. (At about the same time Mooney [40], who proceeded from a hydrodynamic model, arrived, using theoretical methods, at the same conclusion). Robinson s equation contains the relative sedimentation volume value — S, which depends on the particle size distribution of the dispersion... 

Knudsen s model led to the prediction that, if linear kinetics were followed, the age at which 50% of the cement has hydrated is proportional to the fineness constant (or xj in the Rosin/Rammler distribution (equation 4.1) for parabolic kinetics, it predicted that this age is proportional to (K40). Evidence was presented in support of this conclusion for cements considered to follow linear kinetics. The theory did not predict any relation to the breadth of the particle size distribution, which is represented by the slope of the Rosin-Rammler curve. 

In summary, particle size distributions measured at similar conditions using optical and sampling probe-impactor methods are vastly different. No conclusions can be drawn concerning the relative accuracy of these two techniques because of experimental differences. All indications are that the optical counter is operating properly and is applicable and advantageous for in situ measurements. Further experiments comparing the two techniques directly on a common engine will be performed soon to substantiate the particulate formation hypotheses. 

Aquatic suspended particles are usually characterized by a continuous particle size distribution. The distinction between particulate and dissolved compounds, conventionally made in the past by membrane filtration, does not consider organic and inorganic colloids appropriately. Colloids of iron(IIl) and manganese(III,IV) oxides, sulfur, and sulfides are often present as submicron particles that may not be retained by membrane filters (e.g., Buffle et al., 1992). Recent measurements in the ocean led to the conclusion that a significant portion of the operationally defined dissolved organic carbon may in fact be present in the form of colloid particles. 

The effect of oil viscosity on initial emulsion viscosity is not clear from these experiments. The St. Lina crude is about six times as viscous as the California crude. The apparent viscosity of the lower viscosity St. Lina Crude emulsion (2 x 10 moles NaOH/gram oil) is less than 50% greater than the lowest viscosity moderately stable California crude emulsion (4.0 x 10 NaOH). The average particle size of the St. Lina emulsion is 7 microns while that of the Shell crude emulsion is about 3 microns (see Figure 8). Since particle sizes, particle size distributions and types of oil are different, no conclusions can be drain about the influence of oil viscosity. There is, however one fact which should be emphasized, namely that viscosities 600 times lower than that of the crude were observed for 60% St. Lina crude emulsions. 

In conclusion, the particle size distribution may significantly affect the shape of intraparticle diffusion-controlled chromatographic curves, particularly if this distribution is strongly skewed toward the large partide diameters. 

A general conclusion from this is that industry can manufacture a variety of particle size distributions tailored to the requirements of the application. Particle... 

The results obtained for particle-size distribution lead to four conclusions ... 

Iron nanoparticles prepared by pyrolysis of poly(ferrocenylsilanes) inside periodic mesoporous sihca displayed the absence of room-temperature hysteresis in the magnetization curves which shows their superparamagnetic behavior [55]. However, magnetic properties cannot always be easily interpreted. For example, for this material data analysis of magnetization curves resulted in the ambiguous conclusion that either particle size distribution is bimodal, or iron particles have an oxide layer which behaves as small superparamagnetic nanoparticles. So magnetic measurements should be combined with other techniques (probably, in this case, EXAFS may be useful) to allow more accurate evaluation of particle structure. 

Since PCBs are adsorbed on the particle surface, normally coated with a thin layer of organic matter such as humic acid, the concentration in sediment and soil samples is much more likely to be related to the particle surface area per volume unit than to the mass unit. ° For this reason, the concentration of each sample, expressed in pgg dry weight, is normalized by dividing it by the relevant calculated specific surface area, expressed in square meters of surface per cubic centimeter of dry sample (m cm ), as obtained by particle size analysis. Comparisons among concentration values of organic pollutants relevant to samples with different particle size distribution may lead to erroneous conclusions if these are expressed in a conventional way. °... 

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