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摘要: 以天然菱镁矿为原料，添加不同质量分数的NiO粉末，采用高温煅烧法制备了镁砂。利用显气孔体密测定仪、X射线衍射仪、扫描电子显微镜分析NiO粉末掺杂对镁砂熟料烧结性能、物相组成、微观结构的影响。结果表明，在菱镁矿中添加NiO粉末有利于提高镁砂烧结致密性，促进MgO晶粒长大。当不添加NiO粉末时，试样在1600℃烧结前后线变化率为8.72%，体积密度为2.96 g·cm-3，显气孔率为19.2%，MgO晶粒尺寸为1.36 μm；当加入质量百分数为0.75% NiO粉末时，试样烧结前后线变化率为18.06%，制备镁砂体积密度为3.29 g·cm-3，显气孔率为11.5%，MgO晶粒尺寸为3.81 μm。在1600℃对添加NiO粉末的菱镁矿进行烧结，NiO可以与MgO完全固溶，引起MgO晶格畸变，降低晶体活化能，提高MgO烧结致密性能。但添加过多NiO，在短时间内无法与MgO完全固溶，妨碍烧结相的直接接触，影响传质过程，导致样品烧结性能降低。Abstract: The magnesite doped by NiO powders in different mass fractions was prepared by high-temperature calcination using natural magnesite as the raw materials in this study. The effects of NiO doping on the sintered properties, phase composition, and microstructures of magnesite were characterized by apparent porosity tester, X-ray diffractometer, and scanning electron microscope. The results show that, the NiO doping can improve the compactness of magnesite and promote the growth of MgO grain. Without the NiO doping, the line rate, bulk density, and apparent porosity of the magnesite after sintering at 1600℃ are 8.72%, 2.96 g·cm-3, and 19.2%, respectively, and the particle size of MgO is 1.36 μm. The line rate, bulk density, and apparent porosity of the magnesite doped by NiO powders in the mass fraction of 0.75% after sintering at 1600℃ are 18.06%, 3.29 g·cm-3, and 11.5%, respectively, and the particle size of MgO reaches to 3.81 μm. The sintered magnesite doped by NiO powders at 1600℃ can lead to the complete solid solution bewteen MgO and NiO, cause the lattice distortion of MgO, reduce the activation energy of grain growth, and consequentially promote the sintering compactness of the magnesite. But, the over-dose NiO doping may result in the partial solid solution bewteen MgO and NiO within a short time, impede the direct contact of sintered phases, obstruct the mass transfer process, and consequentially lower the sintering compactness of the magnesite.
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Key words:
- magnesite /
- doping /
- sintering properties /
- phase composition /
- microstructures
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图 1 试样线收缩率与NiO质量分数的关系
Figure 1. Relationship between the shrinkage of samples and the content of NiO by mass
图 2 试样烧结性能与NiO质量分数的关系
Figure 2. Relationship between the sintered properties of samples and the content of NiO by mass
图 3 添加不同质量分数NiO烧结镁砂显微形貌：（a）0%；（b）0.25%；（c）0.50%；（d）0.75%；（e）1.00%
Figure 3. Microstructures of magnesite doped by NiO powders in different mass fractions: (a) 0%; (b) 0.25%; (c) 0.50%; (d) 0.75%; (e) 1.00%
表 1 天然菱镁矿石的化学成分（质量分数）
Table 1. Chemical component of the natural magnesite %
MgO CaO Fe2O3 SiO2 Al2O3 灼烧量 45.23 1.69 0.84 1.03 0.13 51.08 
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表 2 NiO质量分数与镁砂MgO晶粒尺寸的关系
Table 2. Relationship between the content of NiO by mass and MgO grain size of magnesite clinker
NiO质量分数/% MgO晶粒尺寸/μm 0 1.36 0.25 2.58 0.50 3.19 0.75 3.81 1.00 3.55
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表 3 镁砂中MgO的晶格常数
Table 3. Lattice constant of MgO of magnesia clinker
NiO质量分数/% 0 0.25 0.50 0.75 1.00 MgO晶格常数/nm 0.420202 0.420286 0.420408 0.420558 0.420560
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