Surface area assessment

In order to compare/contrast methods of surface area assessment, Rodriguez-Reinoso et al. (1989a, b), using two series of activated carbons, made use of several different experimental approaches for their characterization and subsequent comparison. Two series of carbons were prepared, from almond shells and from olive stones which were carbonized in... 

The principal aim of the second edition of this book remains the same as that of the first edition to give a critical exposition of the use of the adsorption methods for the assessment of the surface area and pore size distribution of finely divided and porous solids. 

We therefore felt it timely to attempt a critical exposition and assessment of the common methods for the evaluation of the surface area and pore size distribution of solids from adsorption measurements. Our main concern has therefore been with the use of adsorption data for these purposes rather than with adsorption per se and it is for this reason that our treatment of theoretical matters, whilst sufficiently detailed to bring out the nature of the assumptions underlying the various methods, is not exhaustive we have not set out to write a text-book or a treatise on adsorption, and our choice of material from the literature has been dictated solely by its seeming suitability for the explanation or illustration of the topic under discussion. 

A realistic assessment of biomass as an energy resource is made by calculating average surface areas needed to produce sufficient biomass at different aimual yields to meet certain percentages of fuel demand for a particular country (Table 2). These required areas are then compared with surface areas available. The conditions of biomass production and conversion used ia Table 2 are either within the range of 1993 technology and agricultural practice, or are beheved to be attainable ia the future. 

The effects of data spread should be examined for all individual parameters. These individual effects usually take place simultaneously, and the combined effect is assessed using the root—sum—square (RSS) method. The total additional surface area required to obtain a certain level of design confidence is calculated from... 

Surface Area and Permeability or Porosity. Gas or solute adsorption is typicaUy used to evaluate surface area (74,75), and mercury porosimetry is used, ia coajuactioa with at least oae other particle-size analysis, eg, electron microscopy, to assess permeabUity (76). Experimental techniques and theoretical models have been developed to elucidate the nature and quantity of pores (74,77). These iaclude the kinetic approach to gas adsorptioa of Bmaauer, Emmett, and TeUer (78), known as the BET method and which is based on Langmuir s adsorption model (79), the potential theory of Polanyi (25,80) for gas adsorption, the experimental aspects of solute adsorption (25,81), and the principles of mercury porosimetry, based on the Young-Duprn expression (24,25). 

Almost all common metals and structural steels are liable to corrode in seawater. Regulations have to be followed in the proper choice of materials [16], In addition, there is a greater risk of corrosion in mixed constructions consisting of different metals on account of the good conductivity of seawater. The electrochemical series in seawater (see Table 2-4), the surface area rule [Eq. (2-44)] and the geometrical arrangement of the structural components serve to assess the possibility of bimetallic corrosion (see Section 2.2.4.2 and Ref. 17). Moreover the polarization resistances have considerable influence [see Eq. (2-43)]. The standards on bimetallic corrosion provide a survey [16,17]. 

In vivo biocompatibility was assessed through subcutaneous implantation in Sprague-Dawley rats. PLGA was used as a control polymer. PGS and PLGA implants with the same surface area/volume ratio were implanted in dorsal subcutaneous pockets. A fibrous capsule around PGS (45 pm thick after 35 days implantation) appeared later than that around PLGA (140 pm thick after 14 days implantation). After 60 days of implantation, the implant was completely absorbed with no signs of granulation or scar formation. ... 

Pto,8Reo,2)ML/Pd/C. Although comparing the activity of the Pt/C electrocatalyst with an average particle size of 3.1 nm with that of PtMu/Pd/C electrocatalyst of 9 nm [Zhang et al., 2004] does not provide an adequate activity assessment because of their different surface areas, this does not adversely affect the main conclusions derived from experiments on single-crystal surfaces. 

Other paper collectors that have been used to assess droplet size and distribution patterns include cards such as Kromekote. This was one of several types of collector that provided information on spray deposition in the held, a-Cellulose samplers are fibrous in nature, and include a vertical component to their aspect. This type of collector, along with Mylar cards and other types of card samplers, are often used to provide information on spray coverage as amount of material per unit surface area. 

Table 2.7 lists techniques used to characterise carbon-blacks. Analysis of CB in rubber vulcanisates requires recovery of CB by digestion of the matrix followed by filtration, or by nonoxidative pyrolysis. Dispersion of CB within rubber products is usually assessed by the Cabot dispersion test, or by means of TEM. Kruse [46] has reviewed rubber microscopy, including the determination of the microstructure of CB in rubber compounds and vulcanisates and their qualitative and quantitative determination. Analysis of free CB features measurements of (i) particulate and aggregate size (SEM, TEM, XRD, AFM, STM) (ii) total surface area according to the BET method (ISO 4652), iodine adsorption (ISO 1304) or cetyltrimethylammonium bromide (CTAB) adsorption (ASTM D 3765) and (iii) external surface area, according to the dibutylphthalate (DBP) test (ASTM D 2414). TGA is an excellent technique for the quantification of CB in rubbers. However, it is very limited in being able to distinguish the different types of... 

For small amounts of powder, dissolution of the particulate material can often be assessed (and compared with that of other compounds) by placing the powder in a calorimeter [68] and measuring the heat evolved as a function of time. The surface area must be assessed microscopically (or by image analyzer), and the data must be plotted by a cube root equation [39] ... 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

Given the fact that the effectiveness of magnesium stearate is due, in large part, to its large surface area, these variations should not be overlooked. In addition, studies assessing raw material variability emphasize the need for physical as well as chemical testing of raw materials to ensure uniformity of the final product. 

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