Colloidal dispersions condensation

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

In the specific case of wastewater generated from the condenser water bleedoff in the production of elemental phosphorus from phosphate rock in an electric furnace, Yapijakis [33] reported that the flow varies from 10 to 100 gpm (2.3-23 m /hour), depending on the particular installation. The most important contaminants in this waste are elemental phosphoms, which is colloidally dispersed and may ignite if allowed to dry out, and fluorine, which is also present in the furnace gases. The general characteristics of this type of wastewater (if no soda ash or ammonia were added to the condenser water) are given in Table 9. 

Prepare a little magnesium oleate by treating a solution of sodium oleate with magnesium sulfate. Carefully wash the precipitate free from soluble impurities and dry at about 110°. Suspend 1 g. of the dry salt in 100 cc. of benzene and provide the flask with a reflux condenser. Boil until solution is obtained. Possibly the product is a colloidal dispersion rather than a very perfect solution. It has been found that a very little sodium oleate mixed with the magnesium oleate rendered the emulsions more permanent. 

It is well known that hydrolyzed polyvalent metal ions are more efficient than unhydrolyzed ions in the destabilization of colloidal dispersions. Monomeric hydrolysis species undergo condensation reactions under certain conditions, which lead to the formation of multi- or polynuclear hydroxo complexes. These reactions take place especially in solutions that are oversaturated with respect to the solubility limit of the metal hydroxide. The observed multimeric hydroxo complexes or isopolycations are assumed to be soluble kinetic intermediates in the transition that oversaturated solutions undergo in the course of precipitation of hydrous metal oxides. Previous work by Matijevic, Janauer, and Kerker (7) Fuerstenau, Somasundaran, and Fuerstenau (I) and O Melia and Stumm (12) has shown that isopolycations adsorb at interfaces. Furthermore, it has been observed that species, adsorbed at the surface, destabilize colloidal suspensions at much lower concentrations than ions that are not specifically adsorbed. Ottewill and Watanabe (13) and Somasundaran, Healy, and Fuerstenau (16) have shown that the theory of the diffuse double layer explains the destabilization of dispersions by small concentrations of surfactant ions that have a charge opposite to... 

The above described order-disorder transitions are all three-dimensional phase transitions and occur with essentially infinite sharpness unless the condensed phase exists in a colloidally dispersed state, Recently, it has... 

Colloidal dispersions can be formed either by nucleation with subsequent growth or by subdivision processes [12,13,16,25,152,426], The nucleation process requires a phase change, such as condensation of vapour to yield liquid or solid, or precipitation from solution. Tadros reviews nucleation/condensation processes and their control [236], Some mechanisms of such colloid formation are listed in Table 7.1. The subdivision process refers to the comminution of particles, droplets, or bubbles into smaller sizes. This process requires the application of shear. Some of the kinds of devices used are listed in Table 7.2 [228]. 

The class of mechanical methods used for preparing colloidal dispersions in which particles or droplets are progressively subdivided. See also Condensation Methods. 

Non-porous Zr02 powders can be produced by high-temperature vapour phase condensation methods in this manner discrete spherical particles of c. 4 nm diameter have been obtained (Avery and Ramsay, 1973). It is also possible to prepare colloidal dispersions of sub-micron sized, spheroidal particles of basic salts such as Zr2(OH)6C03 and Zr2(0H)6SO4 with the aid of the carefully controlled sol-gel techniques developed by Matijevic (1988). 

Structure of silica colloids. Present ideas on the state of silica in aqueous solutions are examined in detail in the review by Sretenskaya (1970), where it is mentioned that one of the most typical features is the tendency to polymerize, i.e. to convert from a molecularly dispersed to a colloidally dispersed state. Polymerization is based on the process of condensation of silicol groups Si(OH)4 with liberation of water and as a result formation of the siloxane bonds Si-O-Si. 

Condensation Methods Used for preparing colloidal dispersions in which either precipitation from solution or chemical reaction is used to create colloidal species. The colloidal species are built up by deposition on nuclei that may be of the same or different chemical species. If the nuclei are of the same chemical species, the process is referred to as homogeneous nucleation if the nuclei are of different chemical species, the process is referred to as heterogeneous nucleation. See also Dispersion Methods. 

Nuclei As a solute becomes insoluble, the formation of a new phase has its origin in the formation of clusters of solute molecules, termed germs, that increase in size to form small crystals or particles, termed nuclei. One means of preparing colloidal dispersions involves precipitation from solution onto nuclei, which may be of the same or different chemical species. See also Condensation Methods. 

We may draw a close analogy here between the behaviour of colloidal dispersions and molecular systems. Thus the first case discussed above is analogous to the presence of clusters of molecules in a vapour approaching its condensation point, or in a solution close to saturation. The limiting concentration at which flocculation occurs corresponds to the saturation vapour pressure, or to the solubility of a solid in solution. More complex colloidal systems often exhibit phase behaviour which is paralleled by various phase separation phenomena in molecular systems. Detailed discussion ofthese matters is outside the scope of this book. However, pursuit of these analogies and their interpretation is a currently active area of research. 

The above remarks are couched in very general terms, and apply to some extent to most forms of small metal particle. The available forms are (i) powders, a term which embraces a set of particles of any size, as long as it flows freely (Section 2.2), (ii) aerosols, (iii) colloidal dispersions (Section 2.2), and (iv) supported metals (Section 2.3), including particles formed by condensation of metal atoms onto a flat surface this leads ultimately to a condensed metal film. 

An aerosol is a colloidal dispersion of particles in gas. Fumed or pyrogenic oxides, also known in the case of silica as aerosUs, are powders made by condensing a... 

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