硼对铁焦微观结构的影响

Effects of boron on microstructure of iron coke

为探究硼原子对铁物种在焦炭分子骨架中的分布和价态组成的影响及对铁焦微观结构和强度的促进机理,以添加不同质量分数的硼酸制备的复合铁焦为研究对象,通过光学显微镜、X射线光电子能谱仪、X射线衍射仪等仪器,对比分析了硼添加前后铁焦微晶结构、光学组织、气孔结构和显微强度的变化。结果表明:在硼添加量为0.2%时,所制备的铁焦的Mf+Mm+Mc+Fi结构的含量达到最大,为68.25%,各向同性结构的含量降低,光学组织指数(OTI)和显微强度(MSI)均达到最大,分别为138和49.3,气孔率下降到59%,孔壁厚度增大到20μm;而随着硼添加量的进一步增大,铁焦的OTI和MSI均呈现下降趋势,气孔率上升,孔壁厚度减小。添加适量的硼后,硼原子以层间插入物进入铁焦石墨晶格,从而导致铁焦的稠环增大,中等尺寸各相异性结构含量增加,可促进热解成焦过程中类似粗粒镶嵌等强度较高的显微组织的形成,增大铁焦的壁厚。并且,硼原子对铁焦骨架的掺杂所形成的BC3结构使得铁焦微晶的石墨化程度增强,从而有助于改善铁焦的显微结构强度,有利于增强其稳定性。

In order to explore the impact of boron atoms on the distribution and valence state composition of iron species within the molecular framework of coke, as well as their mecha-nism for enhancing the microstructure and strength of iron coke, composite iron cokes prepared by adding different proportions of boric acid were used as research objects. Using optical micros-copy, X-ray photoelectron spectroscopy, X-ray diffraction and other research methods, the chan-ges in microcrystalline structure, optical structure, and microscopic strength of iron coke before and after boron addition were compared and analyzed. The research results indicate that when the boron addition amount in iron coke is 0.2% (mass fraction), the content of (Mf+Mm+Mc+Fi) structure reaches a maximum of 68.25%, while the content of isotropic structure decreases. Concurrently, the optical texture index (OTI) and microstrength index (MSI) of the iron coke both peak at 138 and 49.3, respectively. Additionally, the iron coke porosity decreases to 59%, and the pore wall thickness increases to 20 μm. As the amount of boron added further increases, both the OTI and MSI values of iron coke show a decreasing trend. The results show that the ad-dition of an appropriate amount of boron allows boron atoms to enter the graphite lattice of iron coke as interlayer insertions, leading to an increase in the dense ring of iron coke and a higher proportion of medium sized anisotropic structures. This process can promote the formation of high-strength microstructures such as coarse-grained inlays, in iron coke during pyrolysis coking process, and increase the wall thickness of iron coke. Moreover, the BC3 structure, formed by the doping of boron atoms into the framework of iron coke, enhances the degree of graphitization of iron coke microcrystals. This enhancement helps improve the microstructure strength of the iron coke and boosts its thermal stability.