The feasibility of synthesis tungsten nitride in magnesium‐tungsten oxide‐melamine ternary system via mechanochemical method

Abstract

Different routes have been investigated to synthesize tungsten (W) – tungsten nitride (W2N) nanocomposite powder by mechanochemical method in magnesium–tungsten oxide–melamine ternary system. In stoichiometric mixture, reduction of tungsten oxide by magnesium took place after 30 minutes of milling in mechanically induced self‐sustaining reaction (MSR). A large amount of heat generated from magnesiothermic reaction, makes the used melamine unstable which causes the formation of undesirable tungsten carbide phase. By separating magnesiothermic reduction from nitride formation reaction, no thermal degradation of melamine occurred; however, milling alone has not brought much change in the used melamine to form tungsten nitride. Dispersion of reaction heat by adding magnesium in three‐stages (during 3 hours of milling) has been capable of preparing maximum value of tungsten nitride phase. According to scanning and transmission electron microscope images, the range of particle size was within 100 nanometer.

Tungsten Nitride, Well‐Dispersed on Porous Carbon: Remarkable Catalyst, Produced without Addition of Ammonia, for the Oxidative Desulfurization of Liquid Fuel

“…[43][44][45] WN x are typically prepared by non-equilibrium nitridation of metallic tungsten under the NH 3 flow. [43,46] The stoichiometric compositions or crystal structures of WN x are mainly dependent on the type of W-precursor (such as metal, oxide, halide, hydride), the starting forms of W (thin film or powder) and on the NH 3 flow rate. [43] Basically, WN x are difficult to synthesize since the incorporation of nitrogen atoms into the tungsten lattice framework is thermodynamically unfavorable under atmospheric pressure.…”

“…[45,47] Additionally, metallic W, WO 3 , W(OH) 3 , and H 2 WO 4 are the most common W-precursors for the synthesis of W 2 N via high temperature nitridation. [46] Herein, we report the synthesis of W 2 N/nitrogen-doped carbon composite from a high temperature pyrolysis of phosphotungstic acid (PTA)-loaded polyaniline (pANI), without external NH 3 flow. The pANI played dual functionalities in the preparation of the composite materials; as the source of nitrogen for nitridation, and as the precursor of nitrogen-doped carbon (also known as pNAI-derived carbon, or pDC [48] ).…”

“…Recently, tungsten nitrides (WN x ) are of great research interest because of their high strength/hardness, high melting point, good chemical stability, good electrical conductivity and low band gap energy (2.2 eV) . WN x are typically prepared by non‐equilibrium nitridation of metallic tungsten under the NH 3 flow . The stoichiometric compositions or crystal structures of WN x are mainly dependent on the type of W‐precursor (such as metal, oxide, halide, hydride), the starting forms of W (thin film or powder) and on the NH 3 flow rate .…”

“…The synthesis of hexagonal W 2 N, for example, usually has been done by the nitridation of W‐precursors under NH 3 flow at a temperature of 500–800 °C . Additionally, metallic W, WO 3 , W(OH) 3 , and H 2 WO 4 are the most common W‐precursors for the synthesis of W 2 N via high temperature nitridation …”