In situ characterization of TiO₂ nanoparticle in chemical vapor condensation reactor

Iron carbide Fe₃C nanoparticles were fabricated by a chemical vapor condensation (CVC), and their structural and magnetic properties were investigated. It was found that the formation of iron carbide nanoparticles strongly depended on reaction temperature and pressure. The iron carbide was formed only above 650 °C at 101 kPa (760 Torr) but never formed in vacuum (1.33 Pa) regardless of reaction temperature. The fabricated iron carbide nanoparticles were spherical with T_c of about 240 °C. While the particles formed at 650 °C (∼30 nm) possessed a typical core–shell structure, those formed at 800 °C (∼50 nm) did not have such structure. The nanoparticles fabricated at 650 °C and 800 °C at 101 kPa, exhibited M_s of ∼125 A m²/kg whereas _iH_c of the former was slightly higher (∼63 kA/m) than that of the latter (∼40 kA/m).

Nanogold clusters synthesized through a chemical process involving 11 or 55 atoms of gold have been widely used for immuno-chemistry probes, in the form of nanoclusters conjugated with biomolecules. The creation of 1 nm size nanogold particles by a materials engineering process has been largely undeveloped. Therefore, the objective of this study is to minimize the size of gold nanoparticle by means of controlling the operating temperature and the chamber pressure during inert gas condensation processing. The size of the gold nanoparticles was resultant of the processing conditions such as the evaporation temperatures and chamber pressures. At a temperature of 1124 °C and pressure of 133 Pa, we were able to obtain approximately 1 nm size nanogold particles.

In inert gas condensation (IGC) evaporation–condensation processing, the effects of IGC convection gas on the crystallographic structure, size and shape of tin oxide nanoparticles were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The phase transformation of tin oxide (II) nanoparticles was also studied after heat treatment at 320 °C. IGC processing was conducted at 1000 °C for 1 h. Oxygen or oxygen and helium mixed gas were used as the convection gas. Metastable tetragonal SnO nanoparticles were obtained at 0.02 kPa of P_O2 and P_(He+O2). The amorphous SnO nanoparticles prepared at 1.3 kPa of P_O2 and P_(He+O2) were explained by the rapid quenching effect of the evaporated nanoclusters. The resultant nanoparticles size was about 10 nm with a round shape. The metastable tetragonal SnO nanoparticles were almost transformed to a stable tetragonal SnO₂ after heat treatment at 320 °C.

In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.