Porosity surface area

Considerable effort has been expended in order to control porosity, surface area and diffusivity of PVC particles and this has led to great improvements over the years in the processability of PVC. 

Carbon electrodes are commercially available in many forms. These include plates, foams, felts, cloths, fibers, spherical and other particles suitable for beds or powders. Graphite or amorphous carbons exhibit quite different performances. Porosity, surface area and pretreatment are important variables to be considered in designing carbon electrodes. 

COATING PAN Pan dimensions. Par speed. TaMet charae- Bed porosity. Surface area Mixino baffles. Perforated area. Bed temperature. 

ArsenX"p is a sorbent that consists of porous (300-1200 pm diameter) polymeric beads that have been impregnated with iron (oxy)(hydr)oxide nanoparticles (Sylvester el al., 2007 Sarkar et al., 2007). The high porosity, surface area, and iron content of the beads allow them to reduce As(V) concentrations to below 10 pgL-1 in water (Tables 7.1 and 7.2). Sulfate, chloride, fluoride, and bicarbonate do not substantially interfere with the removal of As(V). However, like other iron-based sorbents, dissolved silica at pH > 7.5 and phosphate may interfere (Sylvester et al., 2007, 106). ArsenX7 is regenerated with a proprietary process, which involves rinsing the sorbent with a warm caustic solution and then neutralizing the surface charges on the beads (Sylvester et al., 2007, 109). 

In most applications more than one particle is observed. As each individual may have its own particle size, methods for data reduction have been introduced. These include the particle-size distribution, a variety of model distributions, and moments (or averages) of the distribution. One should also note that these methods can be extended to other particle attributes. Examples include pore size, porosity, surface area, color, and electrostatic charge distributions, to name but a few. 

No experimental method provides the absolute value of parameters such as porosity, surface area, pore size, etc. each gives a characteristic value which depends on the principles involved and the probe used. 

Pore volume Porosity Surface area Pd content... 

Table 1. Properties of the titania networks obtained by using polymer gel templates calculated porosity, surface area obtained from nitrogen adsorption, pore, and titania nanoparticle diameters. Adapted with permission from [8]. Copyright 2001 American Chemical Society ...

The immense versatility of the sol-gel process in liquid phase enables control on the size, porosity, surface area, morphology (full or core-shell particle), and hydrophilic-lipophilic balance of the encapsulating silica cage. Not only the conditions of the process can be controlled... 

More recently, columns have been developed where the stationary phase is formed of a porous polymer network inside the capillary. These are called monolithic phases, and have emerged as an alternative to traditional packed bed columns for use in micro-HPLC. They hold many advantages over traditional packed bed columns, being easy to manufacture since the monolith is formed in situ, often via a one-step reaction process, and its properties such as porosity, surface area, and functionality can be tailored. Another major advantage is that they eliminate the need for retaining frits. These columns can be manufactured from a variety of materials, but the most common include sol-gel, methacrylate-based, acrylamide-based, and styrene-based polymeric structures. 

The kinetics of biodegradation is affected by physical parameters like degree of crystallinity, porosity, surface area, and pore size distribution. A striking example is the difference in solubility between amorphous and polycrystalline silicon (Shabir et al. 2011). 

The MBP is a special type of ASD obtained from a controlled coprecipitation process and differs from other ASDs in physicomechanical properties such as porosity, surface area, bulk density, microstructure, flow properties, wettability, etc. Nevertheless, the overall characterization scheme of MBP is the same as any other ASD, which will be described elsewhere in this book. This may include crystallinity by XRD, glass transition temperature evaluation by differential scanning calorimetry (DSC), molecular structure by IR and Raman, solubility assessment and dissolution profile, and micromeritics such as bulk density, particle size, porosity, flowability, etc. Physicomechanical properties of MBP are addressed in Examples of Bioavailability Enhancement section of this chapter. 

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