Melt, particle size effects

Le Meins JF, Moldenaers P, Mewis J (2003) Suspensions of monodisperse spheres in polymer melts particle size effects in extensional flow. Rheol Acta 42 184-190... 

Lauritzen SI, Hoffman JD (1960) Theory of formation of polymer crystals with folded chains in dilute solution. J Res Natl Bur Stand 64A 73-102 Le Meins J-F, Moldenaers P, Mewis J (2003) Suspensions of monodisperse spheres in polymer melts particle size effects in extensional flow. Rheol Acta 42 184—190 Lee BJ, Meat ME (1991) Effect of inclusion shape on the stiffness of nonlinear two-phase composites. J Mech Phys Solids 39 627-649... 

The particle size effect is most noticeable for fuels oxidizers usually have started to melt (or have melted) before the ignition temperature is reached. 

The interest in preparing nanoparticles (size in the 0.1-100 nm range) has increased since it has been realized that they develop quantum and particle size effects, changing drastically their catalytic properties. Other properties change as well when the size of the particles is in the nanorange for instance, silver (mp = 960 °C) melts at 100 °C when it forms particles of 2 nm [58]. 

Buffat P and Borel J P 1976 Size effect on the melting temperature of gold particles Phys. Rev. A 13 2287... 

Skripov V P, Koverda V P and Skokov V N 1981 Size effect on melting of small particles Rhys. Status Solidi A 66 109... 

To develop a more quantitative relationship between particle size and T j, suppose we consider the melting behavior of the cylindrical crystal sketched in Fig. 4.4. Of particular interest in this model is the role played by surface effects. The illustration is used to define a model and should not be taken too literally, especially with respect to the following points ... 

Physical characteristics Molecular weight Vapour density Specific gravity Melting point Boiling point Solubility/miscibility with water Viscosity Particle size size distribution Eoaming/emulsification characteristics Critical temperature/pressure Expansion coefficient Surface tension Joule-Thompson effect Caking properties... 

The concentration of K2TaF7 in the initial melt is the main parameter controlling the particle size and surface area of the reduced primary powder [598]. Typically, the increased concentration of K2TaF7 leads to the formation of coarse tantalum powder. According to Yoon et al. [599], the diluent prevents a strong increase in the temperature of the melt that is caused due to the exothermic effect of the reduction process. Based on the investigation of the reduction process in a K2TaF7 - KC1 - KF system, it was shown that increased amounts of diluent lead to a decrease in particle size of the obtained tantalum powder. 

Based on available results, it can be summarized that the particle size of tantalum powder increases (specific charge decreases) with the increase in temperature, K2TaF7 concentration and excess sodium. In addition, an increase in the specific surface area of the melt and Na/K ratio also leads to the formation of coarser tantalum powder. The most important conclusion is that for the production of finer tantalum powders with higher specific charges, the concentration of K2TaF7 in the melt must be relatively low. This effect is the opposite of that observed in the electrochemical reduction of melts. 

Effects of particle size and pressure on the reactive sintering were studied by Gobran et al. (2004). The synthesis of RuAl was described it was observed that reactive systems containing low-melting constituents such as aluminium are assisted in densification by the formation of a transient liquid phase. Reactive sintering using... 

E. Ercolessi, W. Andreoni, and E. Tosatti, Melting of small gold particles—Mechanism and size effects, Phys. Rev. Lett. 66, 911-914 (1991). 

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