DTA/TG study of tungsten oxide and ammonium tungstate reduction by (Mg + C) combined reducers at non-isothermal conditions

• Reduction of WO3–Mg and APT–Mg systems occurs in the solid state yielding MgO and W.
• Using only C as reducer yields WOx (< 880 °C) or WO2 (~ 960 °C).
• Increasing heating rate shifts the reduction temperature to higher temperature range.
• Adding C into WO3–Mg and APT–Mg systems shifts reduction temperature by about 30–90 °C.

In this work the reaction mechanism in the WO3–Mg/C systems and ammonium paratungstate (APT)–Mg/C systems are studied. As reducer magnesium, carbon or combinations of both are explored. It is shown that in the WO3–Mg system the reduction undergoes by solid–solid mechanism before melting Mg, where metallic tungsten and MgO are formed. Unlike this system, in the WO3–C system mainly WOx (< 880 °C) and WO2 (> 960 °C) and small amount W is formed. In the WO3–Mg–C ternary system reduction temperature shifts to higher temperature range and depends on amount of carbon. Similar to WO3–Mg system, APT–Mg reaction starts and completes in the solid state. Thus, firstly the APT decomposes, then reduction of formed WO3 takes place at ~ 600 °C yielding W and MgO. Likewise to WO3–Mg system adding carbon into APT–Mg mixture shifts reduction temperature to even higher temperature zone which can exceed melting point of Mg and further reduction undergoes with molten magnesium. It is shown that the reduction products are MgO and W.

Adding carbon into binary (WO3(APT)–Mg) system or increasing heating rate leads to shift of the reduction temperature. Using Kissinger and/or Starink methods the activation energy can be calculated based on the shift of Tmax in the DTA curve ( DTA ) Tmax depending on the heating rate (Vh):Figure optionsDownload as PowerPoint slide