Particle Size, Stability

Interestingly, insertion of a trivalent cation like lanthanum stabihses nanoparticles, but it also modifies oxygen migration and vacancy density. In this case however, OSC seems not to be affected by particle size [72]. 

2 Role of Zr02 Additive the Ceria-Zirconia Solid Solution 

Zr02 is the most effective thermal stabihser of Ce02, particularly when it forms a mixed oxide with ceria [40]. By the mid-1990s, TWCs with Ce02—Zr02 mixed 

Remarkably high surface areas can be obtained by carrying out the synthesis in the presence of surfactants (rather than by the conventional co-precipitation) [82]. 

This effect, which persisted after calcination, was ascribed to the presence of an initial surface area, not to a modification of the sintering mechanism. 

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CdS sols of 5 nm particle size stabilized by 10 M sodium hexametaphosphate show a weak green fluorescence 515 nm) besides the red fluorescence at longer... 

For supported-metal catalysts, the questions of interaction with and location of the metal on the support are of important concern, since these factors may be instrumental in determining, for example, the metal particle size and size distribution, the particle size stability to thermal and chemical treatments, and the accessibility of the metal to the reactants of the catalytic process. That these questions are amenable to study using the Mbssbauer effect is the topic of this section. 

Figure 7.14 The change in critical HLB values as a function of added salt concentration, where the salt is either NaCl or Nal. Results were obtained from measurements of particle size, stability, viscosity and emulsion type as a function of HLB for liquid paraffin-in-water emulsions stabilised by Brij 92-Brij 96 mixtures. Data from different experiments showed different critical values hence, on each diagram hatching represents the critical regions while data points actually recorded are shown. Results in (a) show particle size and stability data those in (b) show the HLB at transition from pseudoplastic to Newtonian flow properties (see section 7.3.10) and emulsion type (o/w— w/o) transitions.

T. L. Whateley, G. Steele, J. Urwin and G. A. Small. Particle size stability of Intralipid and mixed total parenteral nutrition mixtures. /. Clin. Hosp. Pharm., 9, 113-26(1984)... 

Whateley TL, Steele G, Urwin J, Small GA. Particle size stability of intralipid and mixed total parenteral nutrition mixtures. J Clin Hosp Pharm 1984 9 113-126. 

Recently, Tiwari and Paul (2011 a) carried out detailed studies on the effect of PP viscosity on the dispersed phase particle size, stability of dispersed phase morphology upon annealing, phase inversion behavior, and changes in the mechanical properties of PP/PP-g-MA/MMT/PS nanocomposites prepared with different molecular weight grades of PP. PP-g-MA was added to PP to facilitate dispersion of organoclay in the nonpolar PP moreover, it also provides better reinforcement effect when PP forms the continuous phase. 

The particle size stability is a special form of the dynamic concentration stability [52]. If the emulsifier is present at a concentration above the critical concentration, new particles will be created. Thus the area growth rate, and therefore the emulsifier consumption, are increased. Then the emulsifier supply by the feed may be in-... 

ABS is also produced via bulk polymerization, with similar characteristics as noted above for HIPS. However, commercial ABS is primarily produced via emulsion polymerization, where SAN is polymerized in the presence of prepolymerized rubber (PB or SBR) emulsions. SAN is grafted to the rubber particles and also crosshnks the rubber particles, providing melt processing particle size stability. The advantage of emulsion polymerization versus bulk polymerization involves the ability to attain lower particle size and thus improved gloss of the injection molded or extruded articles of mamrfacture. ABS can tolerate lower rubber particle size than HIPS without loss of impact strength. In addition to PB and SBR, EPDM and acrylate rubbers have also been employed in the impact modification of PS and SAN. The primary advantage of these rubber modifiers involves the improved weatherabihty and thermal (oxidative) stability. Styrene-maleic anhydride (SMA) copolymers have been impact modified with similar rubber and processes as HIPS and ABS. 

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