Particle measurements, comparison

Fig. 5. Estimated characteristic strength of typical biological particles of interest to biotechnology data are based on in-situ measurements of the minimum stresses necessary to cause permanent breakage of particles. For comparison data are shown based on Van der Waals and pendular liquid bridges between two 10-pm particles, 0.01 pm apart...

Muller, B., and L. Sigg (1990), "Interaction of Trace Metals with Natural Particle Surfaces Comparison between Adsorption Experiments and Field Measurements", Aquatic Sciences 52/1, 75-92. 

Measurements of extinction by small particles are easier to interpret and to compare with theory if the particles are segregated somehow into a population with sufficiently small sizes. The reason for this will become clear, we hope, from inspection of Fig. 12.12, where normalized cross sections using Mie theory and bulk optical constants of MgO, Si02, and SiC are shown as functions of radius the normahzation factor is the cross section in the Rayleigh limit. It is the maximum infrared cross section, the position of which can shift appreciably with radius, that is shown. The most important conclusion to be drawn from these curves is that the mass attenuation coefficient (cross section per unit particle mass) is independent of size below a radius that depends on the material (between about 0.5 and 1.0 fim for the materials considered here). This provides a strong incentive for deahng only with small particles provided that the total particle mass is accurately measured, comparison between theory and experiment can be made without worrying about size distributions or arbitrary normalization. 

The submicron particle number size distribution controls many of the main climate effects of submicron aerosol populations. The data from harmonized particle number size distribution measurements from European field monitoring stations are presented and discussed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distributions of aerosols in the particle sizes most important for climate applications are presented. Annual, weekly, and diurnal cycles of the aerosol number concentrations are shown and discussed. Emphasis is placed on the usability of results within the aerosol modeling community and several key points of model-measurement comparison of submicron aerosol particles are discussed along with typical concentration levels around European background. 

Muller, S.R. and Sigg, L. (1990) Interaction of trace metals with natural particle surfaces comparison between adsorption experiments and field measurements. Aquat. Sci., 52, 75-92. 

Mohr, M., Lehmann, U., Particle Measurement Programme (GRPE-PMP) - Comparison Study of Particle Measurement Instmments for Future Type Approval Applications, EMPA Report, Diibendorf, Switzerland, (2003). 

Measurement by scanning electron microscope of the Zr02 catalysts was performed the micrographs are shown in Fig. 8 (56). It is seen that the samples with the sulfate treatment were cracked into fine particles in comparison with those of the substances without the sulfate treatment. 

In addition. Figure 2 presents a comparison between the voliune of heavy hydrocarbon molecules (neutral and ionized) measured by light absorption 14, 15) and the volume of soot particles measured by molecular beam sampling and electron microscopy (7, 11). These data show that enough heavy molecules exist to account for soot formation, thereby supporting the view that these molecules are probably intermediates of soot. 

Ice particle measurements in the expansion experiment with 40% OC soot aerosol markedly differ from the 16% OC sample. Note that the optical particle spectrometer hardly detects any ice particles. Additionally, extinction signatures of ice are barely visible in the infrared spectra and diere is only a weak intensity increase of the back-scattered laser light in course of the expansion. The number concentration of ice crystals is less than 10 cm, thus < 1% of the seed aerosol particles act as deposition ice nuclei. In contrast to the 16% OC experiment, no precise critical ice saturation ratio can be specified for the 40% OC soot sample. RHi continues to increase to 190% because very little water vapour is lost on the small surface area of the scarce ice crystals. In summary, die comparison of the two expansion experiments provides first evidence that a higher fraction of organic carbon notably suppresses the ice nucleation potential of flame soot particles. 

Equations [4.13] and [4.14] are also supported by some atmospheric measurements. Thus, E. Meszaros (1970) measured the size distribution of the mass of atmospheric sulfate particles by means of a cascade impactor backed up by membrane filters. He found that the geometric mean radius of the distribution averaged by humidity intervals varies as a function of the relative humidity as shown by the points in Fig. 38. The solid line of this figure gives the theoretical relation calculated from equation [4.14] for an ammonium sulfate particle with a dry radius of 0.14 /an, the value found for the geometric mean radius at low relative humidity. The line shows that the particle radius increases by a factor of two at a relative humidity of 80 %. Near 100 % the droplet radius is several times larger than the dry particle size. Comparison of the curve with the experimental points indicates that the behaviour of the atmospheric particle population is well approximated by the theory outlined. It cannot be excluded, however, that the real phase change is less sudden than the theory predicts. 

Figure 11,106. Size-dependence of the quasi-d.c. conductivity a x) of isolated indium particles measured at 10 Ghz. The accuracy of the experimental data is determined by rather broad particle size distribution of the ensembles available. Quantum-size has predicted a particle conductivity proportional to the third power of the diameter d. Calculated values for the classical surface scattering are also shown for comparison. [Reproduced from ref 132 with kind permission of Elsevier.]...

Finally, filtration tests for one of the "optimized confirming precipitation runs were performed to compare the filtration characteristics of the slurry. Figure 10 shows a comparison of the specific cake resistance values obtained fi om this run and compares them to the original process filterability as defined in Figure 4. Figures 11, 12, 13 illustrate a particle size comparison of the two processes based on a chord length PSD, percent fines and volume equivalent size measurement. 

Figure 9.5 Dependence of nanoparticle size on velocity of the inlet streams and polymer concentration (in the solvent feed), for different preformed polymers. Data refer to acetone solvent, if not specified, but some data using THF are shown for comparison CIJM-dl, water-to-solvent volumetric ratio, W/S = 1 particles measured after production and quench (quench volumetric ratio = 0.2).

Matson, U., Ekberg, L. E. Afshari, A. 2004. Measurement of Ultrafine Particles A Comparison of Two Handheld Condensation Particle Counters. Aerosol Science and Technology, 38, 487-495. 

The standard calibration of the MicroCount 05 is based on uniform polystyrene beads traceable to NIST. This provides accurate sizing for a broad range of materials in the ranges above roughly lOpm. At smaUer sizes, the optical properties of the sample influence the sensor response significantly. Tliis is especially true for the smallest particles measured in the scattering channel. When calibrated with polystyrene, the sensor may be used as a comparison instrument. If additional applications information is available, a calibration curve specific to the material can be developed. 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

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