Melting temperature, reduction

Due to their high surface-to-volume ratio, the thermal properties of metallic NPs noticeably differ from those of the bulk form. The important role of the surface in the melting process has long been suspected [308,309] and has recently been confirmed [310] via surface-sensitive measurements of melting. These recent measurements include structural demonstrations of liquid skin formation on flat surfaces below the melting temperature of the interior crystal [311,312] and a dramatic melting temperature reduction for nanometer-sized particles in proportion to the surface-to-volume ratio [313-315]. 

Metal teUurides for semiconductors are made by direct melting, melting with excess teUurium and volatilizing the excess under reduced pressure, passing teUurium vapor in an inert gas carrier over a heated metal, and high temperature reduction of oxy compounds with hydrogen or ammonia. 

Yoon et al. [600] investigated the influence of the process temperature on the yield of tantalum powder and amount of fine fraction obtained. The reduction was performed using K2TaF7 dissolved in a KC1 - KF melt. The melt temperature varied in the range of 800-980°C. The analysis of the obtained results shows that the yield of the process increases at higher temperatures. In addition, higher temperatures lead to a decrease in the amount of fine fraction of tantalum powder produced. Nevertheless, it was noted that solely changing the process temperature does not ensure an improved yield. 

Calorimetric measurements and morphological observations showed that PS-fr-PCL, PB-fr-PCL and PS-fc-PB-fc-PCL copolymers exhibit microphase separation and crystallization if the molecular weight is high enough. Only in PS-fc-PCL diblock copolymers, a shift of the PS glass transition to lower temperatures has been observed. In PS-fo-PB-fo-PCL, the crystallizable block (i.e., PCL) is covalently linked to a rubbery block and it has a free end. For these reasons there is no significant reduction in the melting temperature and... 

Floudas et al. [135] also studied the isothermal crystallization of PEO and PCL blocks within PS-b-PEO-h-PCL star triblock copolymers. In these systems the crystallization occurs from a homogeneous melt Avrami indexes higher than 1 are always observed since the crystallization drives structure formation and does not occur under confined conditions. A reduction in the equilibrium melting temperature in the star block copolymers was also observed. 

One might expect that completely replacing the terephthalate unit in PCT with naphthalene dicarboxylate would make an interesting high-temperature polymer. However, such a polymer cannot be successfully prepared, because its melting point is above its degradation temperature. Reduction of the melting... 

Notice that in order to have a higher coherency among the different systems, we selected the temperatures of the different isothermal sections not on the basis of absolute values but as reduced values of the average melting temperatures (even if the reduction was made in a rather arbitrary way) defining, for a Me-X alloy ... 

In 2004, Rayner and coworkers reported a dynamic system for stabilizing nucleic acid duplexes by covalently appending small molecules [34]. These experiments started with a system in which 2-amino-2 -deoxyuridine (U-NH ) was site-specifically incorporated into nucleic acid strands via chemical synthesis. In the first example, U-NH was incorporated at the 3 end of the self-complementary U(-NH2)GCGCA DNA. This reactive amine-functionalized uridine was then allowed to undergo imine formation with a series of aldehydes (Ra-Rc), and aldehyde appendages that stabilize the DNA preferentially formed in the dynamic system. Upon equilibration and analysis, it was found that the double-stranded DNA modified with nalidixic aldehyde Rc at both U-NH positions was amplified 34% at the expense of Ra and Rb (Fig. 3.16). The Rc-appended DNA stabilizing modification corresponded to a 33% increase in (melting temperature). Furthermore, imine reduction of the stabilized DNA complex with NaCNBH, resulted in a 57% increase in T. ... 

The reaction commences at a temperature above 400° C., before the melting temperature is reached, and the fused product therefore always contains some arsenious oxide.1 When heated in hydrogen, the pentoxide is reduced first to arsenious oxide and then to free arsenic. Similar reduction occurs when it is heated with carbon or phosphorus with sulphur, arsenious sulphide is formed. Arsenic and metallic arsenides result when the pentoxide is heated with alkali metals,2 zinc, lead, iron or most other heavy metals mercury and silver react only at high temperature gold and platinum do not react. 

Temperature development in an extruder channel during melting. In this example, we illustrate reduction in dimensionality of the energy equation to find an equation that would reveal the change of the melt temperature through the gap between the solid bed and extruder barrel during melting, as schematically depicted in Fig. 5.10. To simplify the problem, we assume to have constant properties and a Newtonian viscosity. 

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