Preparation of VN via core-shell precursor method under the intervention of dispersants
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摘要: 采用聚乙烯吡咯烷酮(PVP)优化核壳型钒碳包裹前驱体结构，热处理前驱体获得满足国标VN16牌号的氮化钒(VN)。PVP的引入促进了碳粉在富钒溶液中的均匀分散，有利于多聚钒酸铵(APV) 离子的氢键化，使其吸附于碳粉表面成核和生长，制备的前驱体有包覆完整稳定且厚度均匀适中的APV外壳、碳粉内核及小且均匀的粒径分布。在还原氮化过程中，前驱体到VN的相变过程为：APV→V2O5→V6O13→V7O13→VO2→V3O5→V2O3→(VC) →VN。优化后的前驱体因其细密的核壳包覆结构和均匀的粒度分布，形成了更稳定的相反应界面和更多的反应活性位点，降低了各阶段的反应活化能(Ea)，使还原氮化效率更高，更易向低价VOx和VN转变。与现行碳热还原工艺相比，反应时间缩短75%，N2流量由300 mL/min降低至200 mL/min，耗量约降低40%，显著降低生产成本。Abstract: In this study, polyvinyl pyrrolidone (PVP) is used to optimize the core-shell V@C precursor structure, and the precursor is heat-treated to obtain vanadium nitride (VN) up to the National Standard VN16 grade of China. The addition of PVP promotes both the uniform dispersion of the carbon powders in the vanadium rich solution and facilitates the hydrogen bonding of ammonium polyvanadate (APV) ions, which are adsorbed on the surface of carbon powders for nucleation and growth. The as-prepared precursor by adding PVP has better encapsulated and stable carbon powder core and APV shell with uniform and moderate thickness, as well as small and homogeneous particle size distribution. In the nitridation and reduction process, the phase transition from precursor to VN is as follows: APV → V2O5 → V6O13 → V7O13 → VO2 → V3O5 → V2O3 → (VC) → VN. Due to its more stable core-shell coating structure and more uniform particle size distribution, the optimized precursor forms a more stable phase reaction interface and more active reaction sites, which reduces the reaction activation energy (Ea) at each stage, and makes it more efficient in reducing and nitriding and easier to transition to low-valent VOx and VN. In comparison with current carbothermal reduction process, the reaction time is shortened by 75%, and the flow rate of N2 is reduced from 300 mL/min to 200 mL/min, the usage of N2 is reduced by 40%, significantly reducing production costs.
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Key words:
- vanadium nitride /
- PVP /
- core-shell precursor /
- phase reaction interface
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图 1 不同条件下前驱体的SEM-EDS图
Figure 1. SEM-EDS images of precursors under different conditions
(a) (b) V@Cor；(c) (d) V@Cop
图 3 核壳型钒碳包裹前驱体的合成机理
Figure 3. Synthesis mechanism of core-shell precursors
(a) V@Cor；(b) V@Cop
图 4 不同温度下前驱体热处理过程中原位XRD图谱
Figure 4. In-situ XRD patterns during precursor heat treatment process under different temperatures
(a) V@Cor；(b) V@Cop
图 5 前驱体到VN的吉布斯自由能和反应热
Figure 5. Images of Gibbs free energy and reaction heat of precursor to VN
(a) V@Cor；(b) V@Cop
图 6 N2气氛下不同前驱体50 ℃到
1400 ℃的TG-DTG曲线Figure 6. TG-DTG curves of different precursors from 50 to
1400 ℃ under N2 atmosphere(a) V@Cor；(b) V@Cop
图 7 V@Cor的lnk和T-1线性拟合结果
(a) 第一阶段（0～400 ℃）；(b) 第二阶段（400～850 ℃）；(c) 第三阶段（850～1150 ℃）
Figure 7. Linear fitting results of lnk and T-1of V@Cor
图 8 V@Cop的lnk和T-1线性拟合结果
(a) 第一阶段（0～400 ℃）；(b) 第二阶段（400～850 ℃）；(c) 第三阶段（850～1 150 ℃）
Figure 8. Linear fitting results of lnk and T-1of V@Cop
图 9 前驱体还原氮化制备VN的机理
Figure 9. Preparation mechanism of VN by nitrogen reduction of precursor
(a) V@Cor；(b) V@Cop
表 1 前驱体的激光粒度分布参数
Table 1. Laser particle size distribution parameters of different precursors
前驱体 比表面积
/(m2·kg−1)D(3, 2)
/μmD(4, 3)
/μmDv (50)
/μmDv (90)
/μmV@Cor 326.523 18.38 76.33 46.54 147.03 V@Cop 1272.47 4.92 29.07 10.92 40.53 
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表 2 VN的化学成分
Table 2. Chemical composition of vanadium nitride
% VN产品 V N C S P V@Cor 79.68 16.74 3.46 0.08 0.04 V@Cop 78.93 17.91 2.3 0.07 0.02 国标VN16 77.0～81.0 14.0～<18.0 ≤6.0 ≤0.1 ≤0.06
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