Particle Size and Morphology

Pharmaceutical products are usually subject to quite restrictive particle size and shape specifications. For final products, small (micron-size) particles with a narrow size distribution are desirable because of their short and uniform dissolution time and consequent good bio-availability. Similarly, particle shape influences 

As noted earlier, when crystallization is employed as a crude fractionation step earlier in the purification train, larger particles are desired to facilitate centrifugation or filtration of the slurries. Control of particle size during these crystallizations, therefore, is of great importance due to its influence on subsequent handling steps. 

Growth kinetics from solution often are represented by a power law model in supersaturation. 

For intrinsic growth kinetics C is the interfacial solution concentration of solute. The rate law may be expressed in terms of relative supersaturation, cr. 

The relative supersaturation, ct = (C — C )jC, is proportional to the difference of the solute chemical potential between solution and crystal, RT ln(C/C ), for small values of (C — C )jC under the assumption of an ideal solution. For large supersaturation 

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Xylans from beech wood, corncobs, and the alkaline steeping liquor of the viscose process have been shown to be applicable as pharmaceutical auxiliaries [3]. Micro- and nanoparticles were prepared by a coacervation method from xylan isolated from corncobs [150]. The process is based on neutralization of an alkaline solution in the presence of surfactant, which was shown to influence both the particle size and morphology. They are aimed at applications in drug delivery systems. 

The aim of this chapter is to summarize some of the research findings on xylan, a natural polymer extracted from corn cobs, which presents a promising application in the development of colon-specific drug carriers. Physicochemical characterization of the polymer regarding particle size and morphology, composition, rheology, thermal behavior, and crystallinity will be provided. Additionally, research data on its extraction and the development of microparticles based on xylan and prepared by different methods will also be presented and discussed. 

R Evans. Determination of drug particle size and morphology using optical microscopy. Pharm Technol... 

The influence of catalyst particle size and morphology in phenol hydroxylation is shown in Table VIII and confirms the diffusional constraints in this reaction also. 

The microstructure, properties, and performance of Ni-YSZ anodes depend sensitively on the microscopic characteristics of the raw materials (e.g., particles size and morphology of NiO and YSZ powders). The particle sizes of the starting YSZ powders vary usually from 0.2 to 0.3 pm, whereas those for the NiO powders are 1 pm. The Ni to YSZ volume ratio usually varies from 35 65 to 55 45. For example, the reported Ni to YSZ volume ratios include 34 66 [20, 21], 40 60 [24], 43 57 [22], and 55 45 [23], For a bilayer anode, the functional anode layer in contact with the electrolyte contains 45 to 50 vol% Ni, whereas the anode support layer has 35 to 40 vol% Ni [25, 26], A pore former is usually added to tailor the shrinkage (for the cofiring) and to achieve sufficient porosity (>30 vol%) in the anode or the anode support layer. 

Due to the important relationship between particle size of starting powders and resulting electrode microstructure and corresponding performance, much work has been performed to modify the particle size and morphology of the starting powders used in SOFC processing. Additional methods have been investigated to better control the microstructure and properties of fuel cell components, which are discussed in more detail in Section 6.2. 

Sensitivity Impure HNF shows a value of impact sensitivity of <1 Nm while pure or recrystallized HNF of the same batch exhibits an improvement to the level of >15 Nm. Some researchers have reported friction sensitivity of 25 N. However, the data on impact and friction sensitivity reported by various groups suggest that sensitivity depends not only on purity but also on particle size, shape of crystals and the type of contaminants. There is a lot of variation in the data reported by various investigators and it appears that this variation is attributed to differences in purity, particle size and morphology of HNF synthesized by different groups [84]. 

Detailed experimental studies on these gas-solid combustion reactions reveal the dependence of combustion and propagation characteristics, like front propagation velocity, combustion temperature and degree of conversion, on operating parameters like nitrogen pressure, particle size and morphology of the reactant metal and dilution of the gas and solid phases. From these studies the optimum synthesis conditions for a variety of nitrides are determined and information about the mechanisms of several gas-solid combustion reactions is obtained. With the aid of combustion theory, the apparent values of activation energy for several nitridation reactions are calculated from measured combustion characteristics. 

Bioaccessibility, and therefore oral bioavailability of soil contaminants, depends on soil type and contaminant (Davis et al., 1997 Gr0n and Anderson, 2003 Hamel et al, 1998 Ruby et al., 1999). PTMs occur in soil as a complex mixture of solid-phase chemical compounds of varying particle size and morphology, characterised by variable metal bioavailability. Mineral phases that form under acidic conditions (e.g. lead sulphate, iron-lead sulphate) will tend to be more stable in the acidic conditions of the stomach and hence less bioaccessible. By contrary, mineral phases... 

Surface area which is related to particle size and morphology. 

Duracher D, Sauzedde F, Elaissari A, Perrin A, Pichot C (1998) Cationic amino-containing A-isopropyl acrylamide-styrene copolymer latex particles 1-particle size and morphology vs. Polymerization process. Colloid Polym Sci 276(3) 219-231... 

Gan, Q., Wang,T., Cochrane, C., and McCarron, P. (2005), Modulation of surface charge, particle size and morphological properties of chitosan-TPP nanoparticles intended for gene delivery, Colloids Surf. B. Biointerfaces, 44(2-3), 65-73. 

Suspensions may also be used to deliver nasal formulations, though only rarely, since a number of complicating factors (e.g., particle size and morphology) must be considered. Suspensions offer the advantage of increasing residence time in the nasal cavity, thus possibly augmenting nasal bioavailability. 

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