Reactive gas condensation method

Ullrafine particles (UFPs) of metal and semiconductor nitrides have been synthesized by two major techniques one is the reactive gas condensation method, and the other is the chemical vapor condensation method. The former is modified from the so-called gas condensation method (or gas-evaporation method) (13), and a surrounding gas such as N2 or NII2 is used in the evaporation chamber instead of inert gases. Plasma generation has been widely adopted in order to enhance the nitridation in the particle formation process. The latter is based on the decomposition and the subsequent chemical reaction of metal chloride, carbonate, hydride, and organics used as raw materials in an appropriate reactive gas under an energetic environment formed mainly by thermal healing, radiofrequency (RF) plasma, and laser beam. Synthesis techniques are listed for every heal source for the reactive gas condensation method and for the chemical vapor condensation method in Tables 8.1.1 and 8.1.2, respectively. 

Resistive Heating Combined with Reaction Zone. The simplest way to form nitride UFPs on a laboratory scale is to adopt the reactive gas condensation method with a resistive heating evaporator. UFPs of the Fe-N system were synthesized by evaporating iron from a tungsten basket heated to 1600-2300°C in NH gas pressure of 27 kPa (37). Crystalline phases of a-Fe, y-Fe including about 2.5wt% of nitrogen, and y -Fe4N depend on the NH3 gas pressure and the evaporation temperature. 

---