Polymeric Sol-Gel Method

Dezanneau et al. reported Lai cMn03+a nanocrystalline powders prepared by an acylamide polymerization sol-gel method (Dezanneau et al., 2002a,b, 2003). The composition analysis revealed that for La/ Mn < 0.9 the Mna04 phase was present, while for La/Mn > 0.9, the high oxygen excess led to considerable vancancies on cationic sites. The Curie temperature remained constant at 295 K for the former case, while decreased Curie temperatures were observed for the latter case, due to the increasing amoimt of Mn vacancies. 

The only peak at 254.5 °C observed in the as-received nanoparticles, as shown in Figure 12.5(b), is due to the decomposition of the iron oxide-hydroxide (goethite, FeOOH as proved by theFT-IR spectra) [31,76]. Similar to the TGA observation, a higher decomposition temperature (308.0 °C) was observed in PPy formed with the aid of nanoparticles than that of pure PPy formed without them (298.4 °C). Whereas only one peak was observed in the pure PPy samples, two exothermic peaks were observed in the DTA curves of the nanocomposites. These were due to the decomposition of PPy at 307 °C and the possible phase transition of iron oxide at 480 °C, as reported for the Fc203/PPy nanocomposites fabricated by the simultaneous gelation and polymerization (sol-gel) method [77,78] respectively. As compared with no obvious phase transition in the pure iron oxide nanoparticles, the observed phase transition was due to the intermediate product of PPy [77,78]. 

The surface modification methods of inorganic whiskers mainly include the wet method, dry method, in situ polymerization, sol-gel method, surface coating and coupling agent modification, self-assembly method, and so on. 

---