Colloids formation

The pH at which basic iron(III) formate begins to precipitate depends upon several factors, which include the initial iron and chloride concentration a high concentration of ammonium chloride is essential to prevent colloid formation. It is important to use an optimum initial pH to avoid a large excess of free acid, which would have to be neutralised by urea hydrolysis, and yet there must be present sufficient acid to prevent the formation of a gelatinous precipitate prior to boiling the solution ideally, a turbidity should appear about 5-10 minutes... 

Andersson, K. R., Dent Glasser, L. S. Smith, D. (1982). Polymerization and colloid formation in silicate solutions. In Falcone, J. G. (ed.) Soluble Silicates. ACS Symposium Series No. 194, Chapter 8. Washington, DC American Chemical Society. 

Bates JK, Bradley JP, Teetsov A, et al. 1992. Colloid formation during waste form reaction Implications for nuclear waste disposal. Science 256 649-651. 

Holt KB, Sabin G, Compton RG et al (2002) Reduction of tetrachloroaureate(III) at boron-doped diamond electrodes gold deposition versus gold colloid formation. Electroanalysis 14 797-803... 

In the study of effects of ultrasound on the aqueous reactions of nickel, we found some interesting results, for example, the colloidal formation of Ni-DMG complex and degassing of NH3 during different experiments. When 25 ml of 0.001 M NiSC>4 solution was complexed with 5 ml of 1% dimethyl glyoxime (DMG) in faintly alkaline ammonia medium and sonicated for 30 minutes and compared with another set of 25 ml of complexed solution which was stirred mechanically, a colloidal solution of Ni-DMG complex was formed in sonicated condition. Particles of Ni-DMG complex did not settle even after keeping 3 1 h because of their smaller size, in sonicated solution, whereas in the unsonicated condition large particles of Ni-DMG complex settled down immediately. 

An adsorbing colloid formation method has been used to separate molybdenum from seawater prior to its spectrophotometric determination by the thiocyanate procedure [517]. 

The equilibrium constant of colloid formation (Equation (10.14)) is given by... 

The long-forgotten English chemist Cooper (1759-1839) was the first to give a satisfactory explanation of colloid formation (including the CMC, as below). 

Michaelis, M. and Henglein, A., Reduction of palladium (II) in aqueous solution stabilization and reactions of an intermediate cluster and palladium colloid formation, J. Phys. Chem., 96, 4719, 1992. 

Lewis, L.N. and Lewis, N., Platinum-catalyzed hydrosilylation—colloid formation as the essential step, J. Am. Chem. Soc., 108, 7228, 1986. 

In addition to the ability of HS to form associations with hydrophobic organic species, humic material also reacts readily to form associations with inorganic minerals as well as polar and ionic organic materials. These types of associations are involved in colloid formation with a wide variety of materials [58-61]. 

Microbes are ubiquitous in the subsurface environment and as such may play an important role in groundwater solute behavior. Microbes in the subsurface can influence pollutants by solubility enhancement, precipitation, or transformation (biodegradation) of the pollutant species. Microbes in the groundwater can act as colloids or participate in the processes of colloid formation. Bacterial attachment to granular media can be reversible or irreversible and it has been suggested that extracellular enzymes are present in the system. Extracellular exudates (slimes) can be sloughed-off and act to transport sorbed materials [122]. The stimulation of bacterial growth in the subsurface maybe considered as in situ formation of colloids. 

The major disadvantages of colloidal catalysts studied so far can be attributed to problems in controlling the metal colloid formation (control of particle size, particle size distribution, structure of metal colloids) and stabilization of the prepared particles, which are not yet completely solved. But it is exactly the stability of the nanoparticles, that is decisive for long-term usage during catalytic processes. Moreover for catalytic application, it is extremely important to preserve the large surface of such colloidal systems. 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

Another possible strategy towards colloids stabilized by micellar systems is the use of nonamphiphibc block copolymers containing metal binding ligands in only one of the blocks. For example, a poly(styrene)-fc ock-poly(m-vinyltriphenylphosphine) (PS-b-PPH) was examined with respect to its colloid formation properties (Fig. 6.5) [46]. 

Most frequently, binding protein is added to the incubation mixtures as either serum or purified serum albumin. With human serum albumin, at equilibrium, the acceptor substrate will largely be protein-bound, when the bilirubin albumin molecular ratio is smaller than one (the dissociation constant of the first binding site of purified human serum albumin is approximately 7 X 10 M with 2 X 10 M for two additional binding sites) (J2). The first binding site of albumin, measured with rat serum, has a dissociation constant of about 5 X 10" M (M8). The unbound fraction will normally not exceed the very low solubility of the pigment. Addition of albumin to an alkaline solution of bilirubin, or its addition immediately after neutralization, prevents colloid formation, if the bilirubin albumin molecular ratio is smaller than one (B25). However, colloidal bilirubin, once formed, cannot be redissolved by the addition of albumin (B26). 

At a bilirubin albumin molecular ratio below one the added binding protein will thus act as a kind of buffer, keeping the concentration of unbound substrate sufficiently low to inhibit colloid formation (B25) or precipitation onto bound bilirubin (B26), and will prevent aspecific binding to cell particulates. The binding protein can also be thought of as a reservoir providing a continuous stream of molecularly dispersed sub-... 

Brodersen, R., and Theilgaard, J., Bilirubin colloid formation in neutral aqueous solution. Scand. J. Clin. Invest. 24, 396-398 (1969). 

Ahn, T. M. 1996. Long-Term Kinetic Effects and Colloid Formations in Dissolution of LWR Spent Fuels. US Nuclear Regulatory Commission, NUREG-1564. 

The observed differences between the elements could presumably be attributed to differences in sorption properties of the chemical species present. Unfortunately, with the possible exception of Np, the lack of a complete set of thermodynamic data precludes a quantitative prediction of the concentrations of the various possible species in solution or of the conditions for the formation of solid phases. However, our data suggest that precipitation or colloid formation were the major reactions of Pu, Am and Cm in our solutions and, perhaps, a minor reaction of U. 

This value of K ff) is silently transferred in the Smoluchowski approach to any bimolecular reactions, including three basic processes discussed above A+B— B,A+B—>0 and A+A —> B (for the first time it was applied to the latter reaction describing the colloid formation in liquids). Such an approach... 

Mobile H centres in alkali halides are known to aggregate in a form of complex hole centres [64] this process is stimulated by elastic attraction. It was estimated [65, 66] that for such similar defect attraction the elastic constant A is larger for a factor of 5 than that for dissimilar defects - F, H centres. Therefore, elastic interaction has to play a considerable role in the colloid formation in alkali halides observed at high temperatures [67]. In this Section following [68] we study effects of the elastic interaction in the kinetics of concentration decay whereas in Chapter 7 the concentration accumulation kinetics under permanent particle source will be discussed in detail. 

Below we take into account the non-linear terms in the kinetic equations containing functionals J (coupling spatial correlations of similar and dissimilar particles) but neglect the perturbation of the pair potentials assuming that il(r, t) = l3U(r). This is justified in the diluted systems and for the moderate particle interaction which holds for low reactant densities and loose aggregates of similar particles. However, potentials of mean force have to be taken into account for strongly interacting particles (defects) and under particle accumulation when colloid formation often takes place [67],... 

Despite the extremely low concentrations of the transuranium elements in water, most of the environmental chemistry of these elements has been focused on their behavior in the aquatic environment. One notes that the neutrality of natural water (pH = 5-9) results in extensive hydrolysis of the highly charged ions except for Pu(V) and a very low solubility. In addition, natural waters contain organics as well as micro- and macroscopic concentrations of various inorganic species such as metals and anions that can compete with, complex, or react with the transuranium species. The final concentrations of the actinide elements in the environment are thus the result of a complex set of competing chemical reactions such as hydrolysis, complexation, redox reactions, and colloid formation. As a consequence, the aqueous environmental chemistry of the transuranium elements is significantly different from their ordinary solution chemistry in the laboratory. 

The speciation of the transuranium elements in waters is thus a complex function of hydrolysis, colloid formation, redox reactions, and complexation with available ligands. The solubility (mobility) is, thus, highly dependent on the particular aquatic environment and its characteristics. 

As a practical matter, precipitation is usually carried out in hot, dilute aqueous solutions to allow the slow formation of large crystals. The pH of the solution is chosen to minimize colloid formation. After precipitation, the precipitate is... 

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