Abstract
A new effective method is proposed to prepare vanadium nitride (VN) via carbothermal reduction–nitridation (CRN) of the precursor, obtained by adding carbon black (C) to the stripping solution during the vanadium recovery from black shale. VN was successfully prepared at a low temperature of 1150 °C for only 1 h with a C/V2O5 mass ratio of 0.30 in N2 atmosphere, but a temperature of 1300–1500 °C is required for several hours in the traditional CRN method. The low synthesis temperature and short period for the preparation of VN was due to the vanadium-coated carbon structure of the precursor, which enlarged the contact area between reactants significantly and provided more homogeneous chemical composition. In addition, the simultaneous direct reduction and indirect reduction of the interphase caused by the coating structure obviously accelerated the reaction. The phase evolution of the precursor was as follows: (NH4)2V6O16·1.5H2O → V2O5 → V6O13 → VO2 → V4O7 → V2O3 → VC → VN. The precursor converted to V6O13 and VO2 completely after being calcined at 550 °C, indicating that the pre-reduction of V2O5 in the traditional CRN method can be omitted. This method combined the synthesis of VN with the vanadium extraction creatively, having the advantages of simple reaction conditions, low cost and short processing time.
Highlights
Vanadium nitride (VN) has received increasing attention in recent years due to its typical properties including extreme hardness, high melting point, wear and corrosion resistance, good electric and thermal conductivity, high-temperature stability, as well as good catalytic activity
The traditional procedure for the synthesis of VN is the process of carbothermal reduction– nitridation (CRN) of V2 O5 in N2 at a high temperature of 1500 ◦ C for 3 h with a N2 flow rate of 13.3 × 10−6 m3 · s−1 [11], and at 1400 ◦ C with a N2 flow rate of 50 L·h−1, using a microwave method [12]
In addition to the traditional CRN method, VN was prepared by thermal liquid-solid reaction [14]: Ammonolysis of precursor compounds of metal [7], self-propagating high-temperature synthesis [15], sol-gel method [16], chemical vapor deposition [17], mechanical alloying [18] and other methods [19,20]
Summary
Vanadium nitride (VN) has received increasing attention in recent years due to its typical properties including extreme hardness, high melting point, wear and corrosion resistance, good electric and thermal conductivity, high-temperature stability, as well as good catalytic activity. (Cr,V) (C,N) solid solution powders were synthesized by CRN of the precursor, prepared by heating admixtures of ammonium dichromate ((NH4 ) Cr2 O7 ), NH4 VO3 , and carbon black in distilled water with continuous stirring [22] These methods can reduce the synthesizing temperature greatly, but the production cost remained high due to the use of de-ionized water, NH4 VO3 and nanometer carbon black, indicating the strong demand of a simple, low-cost and low-temperature approach to synthesize VN. To synthesize Pb(Mg1/3 Nb2/3 )O3 ceramic, it may be feasible to prepare the precursor during the vanadium precipitation from the stripping solution in the process of vanadium extraction from black shale, to synthesize VN This method revealed the merits of a low reaction temperature, short period, and a widely available, cheap vanadium source, which make it more practical, economical and efficient in industrial applications. The mechanism of preparing VN from the precursor was discussed through phase analysis, thermodynamic calculation, and thermogravimetric (TG) experiment
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