Size distribution, effect shape

With hysteresis loops of Type HI, the two branches are almost vertical and nearly parallel. Such loops are often associated with porous materials which are known to have very narrow pore size distributions or agglomerates of approximately uniform spheres in fairly regular array. More common are loops of Type H2, where the pore size distribution and shape are not well defined. This is attributed to the difference in adsorption and desorption mechanisms occurring in ink-bottle pores, and network effects. The Type H3 hysteresis loop does not show any limiting adsorption at high relative pressures and is observed in aggregates and macroporous materials. Loops of Type H4 are often associated with narrow... 

Determination of Pore Size Distributions. The shape and range of a GPC calibration curve are, in part, a reflection of the pore size distribution (PSD) of the column packing material. A consideration of the nature of PSDs for the ULTRASTYRAGEL columns to be used in this work is therefore appropriate. The classical techniques for the measurement of PSDs are mercury porisimetry and capillary condensation. The equipment required to perform these measurements is expensive to own and maintain and the experiments are tedious. In addition, it is not clear that these methods can be effectively applied to swellable gels such as the styrene-divinylbenzene copolymer used in ULTRASTYRAGEL columns. Both of the classical techniques are applied to dry solids, but a significant portion of the pore structure of the gel is collapsed in this state. For this reason, it would be desirable to find a way to determine the PSD from measurements taken on gels in the swollen state in which they are normally used, e.g. a conventional packed GPC column. 

The bed void volume available for flow and for gas and liquid holdup is determined by the particle size distribution and shape, the particle porosity, and the packing effectiveness. The total voidage and the total liquid holdup can be divided into external and internal terms corresponding to interparticle (bed) and intraparticle (porosity) voidage. The external liquid holdup is further subdivided into static holdup eLs (holdup remaining after bed draining due to surface tension forces) and dynamic holdup eLrf. Additional expressions for the liquid holdup are the pore fillup Ft and the liquid saturation SL ... 

Tyle (1993) studied oral perception of grittiness and viscosity of synthetic particles (60 mg) suspended in fruit syrups (5 mL). The particles were of different size distributions and shapes angular-shaped garnet 5.2-33.0, rounded micronized polyethylene 7.2-68.9, and flat mica platelets coated with titanium dioxide 28.1-79.6 p,m. There was no effect on the thickness ratings of the studied particulate dispersions. Particles... 

In this section, we discuss the effects of solids addition on the rheology of oil-in-water emulsions, in particular, the effects of solids size (size distribution) and shape (spherical versus irregular). Because the type of the oil used to form an emulsion is important in determining the viscosity of the oil-in-water emulsion, the rheology of the emulsion-solids mixtures is also influenced by the type of oil. Thus, two distinct emulsion systems with added solids will be discussed (1) synthetic (Bayol-35) oil-in-water emulsions 21, 57) and (2) bitumen-in-water emulsions (58). The synthetic oil has a viscosity of 2.4 mPa s, whereas the bitumen has a viscosity of 306,000 mPa s at 25 C. The Sauter mean diameter of the oil droplets is 10 xm for synthetic oil, and 6 xm for bitumen-in-water emulsions. The synthetic OAV emulsions are fairly shear-thinning, whereas the bitumen OAV emulsions are fairly Newtonian. 

Particleboard utilizes residue materials from other wood processing operations. Sawdust and shavings predominate, although most plants are able to use chips or flakes made from roundwood to meet specific strength requirements in the product. Cost is the major driver, with the proportion of high cost material such as chips or roundwood limited to that necessary to meet product requirements. Particle size distribution and shape have become more important as the effect of these variables on product quality has been recognised, leading to reductions in cost. 

Tensile properties of composite propellants depend on the tensile properties of the matrix, concentration of the components, particle size, particle-size distribution, particle shape, quality of the interface between fillers and polymeric binder, and, obviously, experimental conditions (strain rate, temperature, and environmental pressure). Many authors (2, 3) have explained the effect of fillers on the mechanical properties of composites, the importance of the filler-matrix interface on physical properties, and the mechanism of reinforcement of the material. Other efforts have examined the effect of experimental conditions on the failure properties of filled elastomers. Landel and... 

Ceramic monoliths have proven themselves effective as substrates for catalyst washcoat and precious metal because they provide a relatively uniform porous surface. In the catalyst application process, the amount of alumina washcoat picked up depends upon the total porosity, as well as, the size distribution and shape of the pores within the wall. Likewise, the amount of precious metal picked up depends largely upon the amount of porous washcoat on the substrate. Catalyst coaters, therefore, have learned to optimize their process around typical properties of the substrate. However, through subtle variances in raw materials and process steps, variances in porosity occur piece to piece and lot to lot. 

Thus, with adjustments to size, size distribution, and shape, aluminum pigments can be used to create various kinds of "sparkle" effects. Pigment supplier Silberline categorizes five different kinds of aluminum flake effects [9-15] ... 

Other parameters such as size, size distribution, and shape of the particles can also influence the compressibUily and thus the packing density of the cast. Figure 4.20 summarizes the effects of particle size, particle shape, and the degree of... 

The effect of particles and matrix properties on the shear viscosity of LDPE/ GTR blend was also studied by developing a theoretical model to predict the viscosity of the composites as a function of the rheological properties of the matrix, solid concentration, particle size distribution, particle shape, and deformability (Bhattacharya and Sbarski 1998). The real viscosity measurements were found in good agreement with the values predicted below the maximum packing fraction. 

Fig. 5 Relations between with (solid line) and without (broken line) considering the wall effect, for logarithmic Gaussian pore size distributions. The shapes of the two curves get closer to each other when the standard deviation (o ) increases. The limiting displacement factor is ca. exp(1.40)=4.1.

The generalized topics of particle size, particle size distribution, and particle shape have been covered in numerous books and articles.5 jn addition, particle size effects in ceramic processing have also been covered by several authors.In this section we will discuss the aspects of particle size, distribution, and shape as they relate directly to the tape casting process. 

The type of plasticizer and its interaction with PVC is important in selecting the polymer/plasticizer ratio (28). The PVC properties which affect this interaction are size distribution structure, shape, porosity of particles molecular weight and distribution of PVC and other chemicals used in the compounding recipe. Plasticizers are usually added in amounts greater than 20 parts per hundr parts of resin (phr). The reverse effect, unplasticization, is observed at lower concentrations. For most resin-plasticizer combinations at room temperature, a plasticizer threshold concentration must be passed before the normal plasticizer has an effects on physical properties. The extent to which Tg is depressed depends on the amount of plasticizer present. The usual concentration range for plasticizers is 20-85 phr. 

Since SERS is a resonance effect related to the SPR of colloidal particles, its sensitivity is affected by size, shape, and structure of their arrays. The abihty to tailor colloid size, size distribution, and shape motivates examination of the influence of these fectors on SERS [280]. The optimal particle size for the SERS effect was found to be between 30 and 150 nm, with decreasing enhancement in smaller and larger particles [280,281]. Cotton and coworkers checked the influence of the interparticle distance in silver and gold NP (40 nm) arrays on their SERS activity. It was found that only arrays with aggregates (NPs in contact) showed the Raman enhancement, whereas arrays composed of NPs with any interparticle distance had no SERS activity [282]. These findings are in agreement with other research that found that the strongest enhancement comes from molecules situated between particles [278,283]. 

In a pore system composed of isolated pores of ink-bottle shape, the intrusion curve leads to the size distribution of the necks and the extrusion curve to the size distribution of the bodies of the pores. In the majority of solids, however, the pores are present as a network, and the interpretation of the mercury porosimetry results is complicated by pore blocking effects. 

The characteristics of a powder that determine its apparent density are rather complex, but some general statements with respect to powder variables and their effect on the density of the loose powder can be made. (/) The smaller the particles, the greater the specific surface area of the powder. This increases the friction between the particles and lowers the apparent density but enhances the rate of sintering. (2) Powders having very irregular-shaped particles are usually characterized by a lower apparent density than more regular or spherical ones. This is shown in Table 4 for three different types of copper powders having identical particle size distribution but different particle shape. These data illustrate the decisive influence of particle shape on apparent density. (J) In any mixture of coarse and fine powder particles, an optimum mixture results in maximum apparent density. This optimum mixture is reached when the fine particles fill the voids between the coarse particles. 

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