Nanoparticles melting temperatures

Figure 10.5. Size dependence of the melting temperature for (a) Au and (b) CdS nanoparticles. Reproduced from Ref. 51, Copyright 1976, with permission from the American Institute of Physics, and from Ref. 52, Copyright 1992, with permission from the AAAS, respectively.

The results presented here also indicate the need to measure the melting temperature of Co nanoparticles at high temperatures. Our group is working toward achieving this goal using synchrotron sources. 

The melting temperature of a nanoparticle dramatically decreases and in some cases, it may be nearly 300 k lower than for bulk material [101]. 

Another example of the stable nonequilibricity of the catalytically active components is the subnormal melting temperature of metal nanoparticles in the course of amorphous carbon graphitization they catalyze (see Figure 4.12). The process follows the stepwise reaction... 

TEM results directly evidence on appearance of nanoparticles together with specific r elief o f t he matrix i n t he p article s unrounding. D iameter o f t he p articles varies in the range of 20-100 run. Nanoparticles are usually located in the specific cavities those can appear due to very different melting temperatures of matrix and semiconductors (AT>300 K). 

Fig. 1 Melting of sodium nanoparticles (from Martin et al. [32]). The metal has bulk melting temperature Tin,bulk = 371K...

There are some examples of the nanoparticle formation in polymers by metal hydroxide decomposition [102]. The thermal decay of silver hydroxide ammonia solution in the isotactic PP melt (temperature range 543-563 K in polymethylsiloxane) occurs according to the following scheme ... 

Nanocalorimetry has been used by Olson and coworkers to investigate size-dependent melting of Bi nanoparticles. It has been discovered that for particles smaller than 7 nm the measured melting temperatures are about 50 K above the value predicted by the homogeneous melting model. The discrepancy is analyzed in terms of a possible size-dependent crystal structure change and the superheating of the solid phase [18],... 

FIGURE 13.26 Nanoparticle melting (a) computer modeling for Au (b) showing the lattice parameter and melting temperature changes as the size of CdS nanoparticles decreases. 

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