Hydrothermal Synthesis of Todorokite and Its Influencing Factors
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摘要: 钙锰矿具有3× 3的大隧道构造, 广泛分布于大洋锰结壳和锰结核等环境中, 其性质和成因倍受关注.以改进方法制备的水钠锰矿(birnessite)为前驱物, Mg2+交换后得到Mg-水钠锰矿(或称布塞尔矿, buserite), 经热液处理合成了结晶度高的单相钙锰矿(todorokite), 采用X-射线衍射(XRD)、透射电镜(TEM)和选区电子衍射(SAED)等技术探讨了热液温度、体系压力和处理时间等因素对钙锰矿合成的影响.结果表明: 合成的钙锰矿与天然钙锰矿有相同的形貌和生长特征, 呈纤维状, 沿120°三连晶生长, 平均化学组成为Mg0.16MnO2.07 0.82H2O.在实验条件下, 热液温度和处理时间是影响钙锰矿合成的主要因素; 而通过改变高压釜的填充度引起体系压力的变化对钙锰矿合成的影响较小, 体系压力并不是钙锰矿形成的主要影响因素.热液温度越高, Mg-水钠锰矿转化为钙锰矿的速率越快, 完全转化为钙锰矿所需的处理时间越短.热液温度分别为120℃、160℃和200℃时, Mg-水钠锰矿完全转化为钙锰矿所需的时间分别为6 h、4 h和2 h; 但热液温度高于160℃时, 易生成水锰矿杂质.延长处理时间与提高热液温度具有相似的影响规律.这进一步明确了钙锰矿的生成条件, 可为阐明钙锰矿的形成机制和促进其在材料科学中的应用提供理论依据.Abstract: Todorokites are a family of 3×3 large tunnel-structured manganese oxides, widely occurring in geological settings such as marine manganese crusts and manganese nodules.In this paper, birnessite prepared by a modified method was taken as the precursor to synthesize todorokite. Birnessite was exchanged with Mg2+ and transformed to Mg-birnessite(or buserite). Mg-birnessite was hydrothermally treated to synthesize well-crystallized pure todorokite. The effects of hydrothermal temperature, system pressure and treatment time on the synthesis were investigated with the techniques of XRD, TEM and SAED. Results showed that the synthetic todorokite crystal consisted of fibers, grew at 120° to form trilling patterns, and its morphology and growth characteristics were the same as those of naturally occurring todorokite. Its average composition was Mg0.16MnO2.07 0.82H2O. Variation of system pressure caused by changing the filling ratio of the autoclave had little effect on the synthesis; pressure was not an important factor on todorokite formation. Increasing hydrothermal temperature accelerated the transformation rate of Mg-birnessite to todorokite, and synthetic todorokite crystallinity increased. When hydrothermal temperatures were at 120℃, 160℃ and 200℃, it took 6 h, 4 h and 2 h respectively to complete Mg-birnessite to todorokite transformation. Hydrothermal temperature higher than 160℃ yielded manganite impurity. Elongating treatment time had similar effects to an increase in hydrothermal temperature. These results can provide theoretical clues for further revealing the origination of todorokite in environments and for prompting applications of todorokite in the area of material science.
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Key words:
- todorokite /
- birnessite /
- hydrothermal synthesis /
- influencing factors
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图 1 不同条件下合成钙锰矿的XRD图谱
Fig. 1. XRD patterns of the synthetic todorokite in different conditions
图 2 160 ℃热液处理4 h合成钙锰矿的透射电镜像
a.形貌图; b.三连晶的高倍电镜像和[001]取向电子衍射图
Fig. 2. TEM images of synthetic todorokite for 4 h at 160 ℃
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