Solid phase reaction and diffusion behavior of V2O5/Cr2O3-CaO system based on calcification roasting of chromium–containing vanadium slag
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摘要: 为探究钒铬渣钙化焙烧过程钒、铬组元与钙反应能力的差异，在热力学分析基础上，以V2O5、Cr2O3、CaO纯物质为原料，采用恒温焙烧法分别制备出V2O5-CaO与Cr2O3-CaO扩散偶。利用扫描电镜与能谱仪观测不同恒温时间后扩散界面的微观形貌以及产物层元素分布，分析恒温时间对固相界面反应的影响，并利用wagner方程对体系互扩散系数进行计算。结果表明：在空气气氛中873 K恒温焙烧9 h后，V2O5-CaO扩散偶界面产物层清晰，厚度与时间的平方根存在线性关系，说明该固相反应由扩散控速，产物以CaV2O6为主。而相同焙烧条件下，Cr2O3-CaO间未见明显的界面产物层，说明V2O5-CaO间固-固界面反应能力更强，其互扩散系数量级为10−10 cm2·s−1。Abstract: The difference in combining ability with calcium between vanadium and chromium in the calcification roasting process of chromium-containing vanadium slag was investigated by V2O5-CaO and Cr2O3-CaO diffusion couples which were prepared by roasting at constant temperature with V2O5, Cr2O3 and CaO as raw materials. The microstructure of the diffusion interface and the element distribution of the product layer were observed and detected by SEM-EDS. The effect of roasting time on solid phase interface reaction were analyzed, and the diffusion coefficient was calculated by Wagner equation. The results show that a recognizable product layer at the interface of the V2O5-CaO diffusion couple can be found by roasting at 873 K for 9 h in air atmosphere. The thickness of the product layer is linearly related to the square root of roasting time, indicating a diffusion-controlled process for the solid phase reaction, with the product layer mainly composed of CaV2O6. Under the same roasting condition, no obvious product layer is formed in Cr2O3-CaO diffusion couple. It suggests that the solid-solid interface reaction ability between vanadium and calcium is stronger than that of chromium and calcium. The order of magnitude of diffusion coefficient of V2O5-CaO diffusion couple is 10−10 cm2·s−1.
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图 2 V2O5/Cr2O3-CaO体系反应的热力学关系图
Figure 2. ∆Gθ-T graph of the formation reaction of V2O5/Cr2O3-CaO system
图 3 V2O5-CaO扩散偶873 K恒温焙烧0～9 h线扫描分析
Figure 3. Line scanning of V2O5 -CaO diffusion couples roasted at 873 K for 0～9 h
图 4 V2O5 -CaO扩散偶873 K恒温焙烧9 h的背散射电子像与元素分布
Figure 4. BSE and elements distribution of V2O3-CaO diffusion couple roasted at 873 K for 9 h
图 6 Cr2O3-CaO扩散偶873 K恒温焙烧15 h线扫描分析
Figure 6. Line scanning of Cr2O3-CaO diffusion couple roasted at 873 K for 15 h
图 7 Cr2O3-CaO扩散偶873 K恒温焙烧15 h的背散射电子像与元素分布
Figure 7. BSE and elements distribution of Cr2O3-CaO diffusion couple roasted at 873 K for 15 h
图 8 873 K条件下V2O5-CaO扩散偶产物层厚度与时间关系
Figure 8. Relationship of the product layers of V2O5-CaO diffusion couple with time at 873 K
图 9 V2O5-CaO扩散偶873 K恒温焙烧9 h的浓度分布曲线
Figure 9. Concentration distribution curve of V2O5-CaO diffusion couple for 9 h at 873 K
表 1 扩散试验条件
Table 1. Conditions of diffusion experiment
扩散偶 温度/K 气氛 恒温扩散时间/h V2O5-CaO 873 空气 0，3，6，9 Cr2O3-CaO 873 空气 0，3，6，9，12，15 
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表 2 873 K恒温焙烧9 h的V2O5-CaO扩散偶互扩散系数
Table 2. Diffusion coefficient of V2O5-CaO diffusion couple at 873 K for 9 h
恒温时间/
hD×1010(NCa=0.02±0.002)/
（cm2∙s−1）D×1010(NCa=0.05±0.002)/
（cm2∙s−1）D×1010(NCa=0.12±0.01)/
（cm2∙s−1）D×1010(NCa=0.48±0.01)/
（cm2∙s−1）9 0.196 0.141 1.137 0.017
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