Advances in Earth Science ›› 2011, Vol. 26 ›› Issue (5): 507-515. doi: 10.11867/j.issn.1001-8166.2011.05.0507

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The Origin and Simulation of Nanophase Iron in Lunar Soil

Tang Hong 1, 2, Li Xiongyao 1, Wang Shijie 1, Li Yang 1, 2   

  1. 1.Lunar and Planetary Science Research Center,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang550002, China; 2. Graduate University of the Chinese Academy of Sciences, Beijing100039, China
  • Received:2010-09-02 Revised:2010-12-08 Online:2011-05-10 Published:2011-05-10

Tang Hong, Li Xiongyao, Wang Shijie, Li Yang. The Origin and Simulation of Nanophase Iron in Lunar Soil[J]. Advances in Earth Science, 2011, 26(5): 507-515.

Unprotected by atmosphere and magnetosphere, exposed lunar surface has been subjected to several harsh space processes. Among them, meteoroids and energetic charged particles are the dominant forces that shape the lunar surface. Collectively, these processes are known as “space weathering”. Nanophase iron (np-Fe0) particles produced by space weathering have been widely observed in the lunar soil, which could have important effects on the physical, chemical and optical properties of lunar soil. In studies of lunar samples, it is found that np-Fe0 occurs in two main petrographic settings in lunar soil: as inclusions within agglutinitic glass and as inclusions in thin amorphous rims surrounding soil grains. Meteorites bombardment, especially micrometeorites bombardments could locally melt the lunar surface materials which saturat with hydrogen implanted from solar wind, and then reduce the ferrous minerals to metallic irons in agglutinatic glass. In previous studies, the size of np-Fe0 particles was found to be about 3~33 nm. But recent studies show that the np-Fe0 particles in agglutinatic glass are much larger, and most of them are about 50~200 nm in size and finely dispersed. Vapor deposition from micrometeorites bombardments and sputtering deposition from solar wind and cosmic rays produce np-Fe0 particles in the amorphous rims around the lunar grains surfaces. The size of np-Fe0 particles in the rim is ranged from several nanometers to tens of nanometers. Most of them are about 10nm. To investigate the relationship between np-Fe0 and various properties of lunar soil, simulation of the production process of np-Fe0 by space weathering is necessary because of the scarcity of lunar samples for research purpose and the complexity of the lunar soil. At present, there are three main methods to simulate the lunar soil analogs with the np-Fe0 particles. Laboratory simulation of np-Fe0 production in lunar space weathering deserves a more realistic approach to model the production process of np-Fe0 in lunar soil. Combining the formation and characteristics of np-Fe0 in lunar soil, we discuss the feasibility of two new experimental methods, which use microwave heating and magnetron sputtering to simulate np-Fe0 in the glass and on the grains surfaces respectively. Microwave heating can heat materials such as ilmenite which have a large dielectric loss to high temperature at a very fast heating rate, which might be a good method to simulate the production of np-Fe0 in the glass phase by reducing ferrous materials to metallic iron. Magnetron sputtering technique is a physical vapor deposition technique, which is similar to the deposition process of vapor deposition and sputtering deposition in lunar space weathering. The primary results of these two experimental simulations show that the characteristics of np-Fe0 produced in the simulations are in consistent with those of lunar samples documented in literature. Simulation of np-Fe0 is very important to remote sensing, lunar science and lunar exploration.

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