Particle surface area

Specific surface area of cellulose fiber is not large, compared to that of fine mineral fillers. Although the latter often have it in dozens of meter square per grams, cellulose fiber has it around 1 m /g. For example, hardwood has particle surface area of 1.01 m /g, softwood—1.34 m /g. Flax fiber has surface area between 0.31 and 

88 m /g, depending on a mode of its treatment [134]. Furthermore, specific surface area principally depends on which tool was used for its measurements—a gas, water, mercury, or large organic molecules. The larger the molecule used for the measurement, the lower the specific surface area. For example, specific surface area of cellulose fiber accessible for water in wet state is 100-200 m.  

---

Monomer compositional drifts may also occur due to preferential solution of the styrene in the mbber phase or solution of the acrylonitrile in the aqueous phase (72). In emulsion systems, mbber particle size may also influence graft stmcture so that the number of graft chains per unit of mbber particle surface area tends to remain constant (73). Factors affecting the distribution (eg, core-sheU vs "wart-like" morphologies) of the grafted copolymer on the mbber particle surface have been studied in emulsion systems (74). Effects due to preferential solvation of the initiator by the polybutadiene have been described (75,76). 

M ass Transfer. Mass transfer in a fluidized bed can occur in several ways. Bed-to-surface mass transfer is important in plating appHcations. Transfer from the soHd surface to the gas phase is important in drying, sublimation, and desorption processes. Mass transfer can be the limiting step in a chemical reaction system. In most instances, gas from bubbles, gas voids, or the conveying gas reacts with a soHd reactant or catalyst. In catalytic systems, the surface area of a catalyst can be enormous. Eor Group A particles, surface areas of 5 to over 1000 m /g are possible. 

Ga.s-to-Pa.rticle Heat Transfer. Heat transfer between gas and particles is rapid because of the enormous particle surface area available. A Group A particle in a fluidized bed can be considered to have a uniform internal temperature. For Group B particles, particle temperature gradients occur in processes where rapid heat transfer occurs, such as in coal combustion. 

Fundamental models correctly predict that for Group A particles, the conductive heat transfer is much greater than the convective heat transfer. For Group B and D particles, the gas convective heat transfer predominates as the particle surface area decreases. Figure 11 demonstrates how heat transfer varies with pressure and velocity for the different types of particles (23). As superficial velocity increases, there is a sudden jump in the heat-transfer coefficient as gas velocity exceeds and the bed becomes fluidized. 

Surfa.ce, Any reaction between two powder particles starts on the surface. The amount of surface area compared to the volume of the particle is, therefore, an important factor in powder technology. The particle—surface configuration, whether it is smooth or contains sharp angles, is another. The particle surface area depends strongly on the method of production, as shown in Table 1. The method of production usually determines the particle shape. 

Characterization. The proper characterization of coUoids depends on the purposes for which the information is sought because the total description would be an enormous task (27). The foUowiag physical traits are among those to be considered size, shape, and morphology of the primary particles surface area number and size distribution of pores degree of crystallinity and polycrystaUinity defect concentration nature of internal and surface stresses and state of agglomeration (27). Chemical and phase composition are needed for complete characterization, including data on the purity of the bulk phase and the nature and quaHty of adsorbed surface films or impurities. 

If requited, the drydown can be hastened by increasing desiccant mass, particle surface area, or mass-transfer coefficient. The mass-transfer coefficient can be altered to some extent by the design of the desiccant container. 

At high Reynolds numbers the friction factor becomes nearly constant, approaching a value of the order of unity for most packed beds. In terms of S, particle surface area per unit volume of bed,... 

Airstream neutralization of acid aerosols by NH3 present in the airway-lumen reduces the health risk associated with acid particles by reducing the acid concentration prior to particle deposition.- In addition, the liquid lining of the respiratory tract probably acts as a chemical buffer," further reducing the health hazard posed by inspired acid particles. Principal factors controlling airstream neutralization of acid aerosols, which is considered to be a diffusion-limited process, are particle surface area, and particle... 

Since NFI3 is highly water-soluble and neutralization within the droplet occurs rapidly, " the rate-limiting step in acid neutralization is normally NH 3 transport to the air/droplet interface, which is dependent on [NH3]4 and particle surface area. At high [NH3J4, the rate of NH, uptake across the air/droplet interface is given by... 

Particle formation in the early stages of a batch reaction is normally quite rapid. Hence the particle surface area produced is able to adsorb the free emulsifier quite early in the reaction (2 to 10% conversion) and particle formation ceases, or at best slows to a very low rate. Particles formed in the beginning of the reaction would have approximately identical ages at the end of the batch reaction. These particles would be expected to be nearly the same size unless flocculation mechanisms, stochostic differences, or secondary nucleation factors are significant. 

The efficiency of extraction was observed to be inversely proportional to the corn cob particle size. This was expected because the size reduction corresponds to an increase in total particle surface area. An increase in the time of the alkaline extraction and in the NaOH concentration also improves the efficiency of xylan extraction. This happened because when the NaOH concentration was lower, the xylan present in corn cobs could not be fully dissolved in the solution. Thus, it resulted in lower efficiency of xylan extraction. However, when the NaOH concentration was higher than 2 M, the yields decreased with continuously increasing of the NaOH concentration. This is probably due to the alkaline degradation of xylan chains, proceeding at the higher NaOH concentration, which indicated that the ideal NaOH concentration in the extraction was between 1.5 and 1.8 M (Unpublished data). 

Surface area of the sphere with same volume as particle Surface area of the particle... 

In a recent comprehensive study, Chhabra, Agarwal, and Sinha(27) have found that the most satisfactory characteristic linear dimension to use is the diameter of the sphere of equal volume and that the most relevant characteristic shape is the sphericity, (surface area of particle / surface area of sphere of equal volume). The limitation of this whole... 

Particle surface area, shape and texture (morphology)... 

Ap is the particle surface area and therefore the effective diameter becomes... 

The polymer particles decrease in stability during intervals II and in since the total polymer particle surface area increases and the coverage of the surface with surfactant decreases. The relative decrease in particle stability appears to be insufficient to cause coalescence as long as stirring is maintained since N is generally observed to be constant. In some systems, however, the stability decreases sufficiently to cause the particles to coalesce and N decreases with conversion [Blackley, 1975]. 

Body, J.E. Persson, P. Sjdberg, S. (2000) Benzene carboxylate surface complexation at the goethite (a-EeOOH)/water interface. III. The influence of particle surface area and the significance of modelling parameters. J. Cod. 

The absorption fraction of a particle is related to the volume of the particle. Thus, the larger the volume of a particle, the more of the incident light is absorbed. In contrast, reflectance is related to the particles surface area, being in turn dependent on material porosity. The absorption/remission function relates to the fraction of absorbed light, the fraction of remitted (or back scattered) light, and the fraction of light transmitted by a representative layer... 

Reaction in the bulk. Reaction can occur in solution close to the surface or throughout the bulk of the liquid phase, depending on the speed of the reaction compared to diffusion. We shall see that whether the reaction occurs close to the surface or throughout the bulk has important implications for the kinetics, since in the former case, the reaction depends on the particle surface area, whereas in the latter it depends on the particle volume. 

---