天然钒钛磁铁矿中出溶现象的高分辨电镜观察

HREM OBSERVATION OF THE EXSOLUTION OF Fe(V,Ti)_2O_4 IN NATURAL SAMPLE

利用高分辨电子显微镜及微区X射线能谱成分测定的方法,对含钒的天然磁铁矿的精细结构进行了研究。结果表明,[110]方向的高分辨像清楚地显示钒钛磁铁矿在磁铁矿基体中以共(110)面紧密连生的方式与基体共生,形成波状连生体。这种成份调制波结构表明它们是出溶产物。

The microstructures of magnetite containing vanadium and titanium have been investigated by means of high resolution electron microscopy(HREM). The observed magnetite was selected from a mantle-derived rock in basalts in Panzhihua, Sichuan Province, The typical feature of exsolution was detected and examination of energy dispersive analysis of X-ray on this area showed mainly iron,vanadium and titanium presence. Simulated image confirms that there is a sharp different contrast in magnetite and coulsonite areas so that the fine wave-like microstructure in[110]struetural images as constructed by the intermate intergrowth of magnetite and coulsonite or ulvospinel along the[110] direction instead of the [111] direction as reported before as a result of the exsolution of coulsonite or ulvospinel in matrix.The length of composition modulated wave is about tens of Angstroms and the feature suggests the exsolution having close relationship with nucleation and growth mechanism. The planar defect found in the dame field could supply favourable positions for heterogeneous nucleation of coulsonite or ulvospinel and had effective action for these nucleations coarsing along them in the process of decomposition.