Size and morphology of particles

Although the elementary composition of particulates has been widely reported (Parsons and Strickland, 1962 Menzel and Ryther, 1964 Holm-Hansen et al., 1966), this is not the case for the biochemical composition. The difficulty in collecting enough material for such studies is probably the cause of this discrepancy. Particles are more often than not composed of both mineral and organic substances and their elemental composition is not consistent. The separation of organic and mineral constituents reveals that organic particles represent 75—80% of the suspended matter (Lascaratos, 1974). 

More widely used for descriptive purposes is the C/N ratio. From 5—8 in surface waters it increases to IB-12 with depth, indicating that proteins are more readily utilized than are carbohydrates. Handa (1970) and Handa et al. 

In some works (e.g. Parsons and Strickland, 1972), some discrepancies appear between the proportions of the biochemical constituents and the total organic carbon. This raises questions about the very nature of suspensions, especially in the deep sea. 

With the exception of the works of Handa and co-workers, most of the determinations of the biochemical composition of suspensions have been made by direct colorimetric measurements. However, the molecular structure of particulate organic matter may be such that terminal functional 

As seen, we have very little information about the chemical composition of organic particles. It is obvious that we have much to learn about the chemical processes in sea water from the investigation of the chemical composition of dissolved and particulate organic matter. The following decades will probably give many answers to the numerous remaining questions. 

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Table 2 Qualitative Description of the Effect of Different Process Parameters on the Size and Morphology of Particles Obtained by Antisolvent Precipitation "...

Flow rate is the main parameter affecting the size and morphology of particles. Several studies have shown that the particle diameter can be controlled by flow rate and electrical conductivity. Ganan-Calvo proposed a theoretical model that reasonably agrees with the experimental results ... 

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. 

AFM has been used in only a few studies to explore the sizes and morphology of airborne particles (e.g., Friedbacher et al., 1995 Posfai et al., 1998). In this case, atomic scale resolution is not used, but rather much lower resolution that provides information on particle sizes and shapes in the micron and submicron size range under ambient conditions. This has the advantage that effects due to the application of vacuum... 

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]. 

Electron Microscopy. Electron microscopy is one of the most important physical methods for the characterization of finely divided solids. It allows direct viewing of the shape and morphology of particles in this order of magnitude, primary particle size, particle size distribution, and aggregation. 

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. 

Hydrothermal reactions typically produce nanometer-sized particles that can be quenched to form a nanoparticle powder or cross-linked to produce nanocrystalline stmctures (Feng and Xu, 2001). Hydrothermal conditions allow for reduction in solubilities of ionic materials and thus more rapid nucleation and increased ion mobility, resulting in faster growth. Via judicious choice of the hydrothermal conditions, a measure of control can be exerted over the size and morphology of the materials. As mentioned earlier, the viscosity and ionic strength of solvents is a function of the temperature and pressure at which the reaction is carried out. Other experimental parameters, such as the precursor material and the pH, have... 

In preparing fine particles of inorganic metal oxides, the hydrothermal method consists of three types of processes hydrothermal synthesis, hydrothermal oxidation, and hydrothermal crystallization. Hydrothermal synthesis is used to synthesize mixed oxides from their component oxides or hydroxides. The particles obtained are small, uniform crystallites of 0.3-200 jim in size and dispersed each other. Pressures, temperatures, and mineralizer concentrations control the size and morphology of the particles. In the hydrothermal oxidation method, fme oxide particles can be prepared from metals, alloys, and intermciallic compounds by oxidation with high temperature and pressure solvent, that is, the starting metals are changed into fine oxide powders directly. For example, the solvothermal oxidation of cerium metal in 2-mcthoxycthanol at 473-523 K yields ultrafine ceria particles (ca 2 nm). 

The reinforcement of rubber by the presence of active fillers is a complex phenomenon that depends on the characteristics of the elastomer network and the properties of the fillers. The influential properties are the particle size, the morphology of particle aggregates, and the surface properties. The role of the geometrical characteristics of the tiller is well understood, whereas the significance of the surface properties is more difficult to analyze. This situation stems essentially from the lack of adequate methods to analyze the surface of such small particles and from the fact that fillers differ from each other and need to be considered individually. 

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