Space radiation processing of sulfides and silicates in primitive solar systems materials: Comparative insights from in situ TEM ion irradiation experiments
Space radiation processing of sulfides and silicates in primitive solar systems materials: Comparative insights from in situ TEM ion irradiation experiments
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原始太阳系材料中硫化物和硅酸盐的空间辐射处理：原位 TEM 离子辐照实验的比较见解
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发表时间：
2011
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通讯作者：
L. Keller
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作者：
R. Christoffersen;L. Keller
摘要：在星周、星际和原恒星环境中包含尘埃颗粒的矿物颗粒可能会发生非晶化和其他固态转变，这些转变来自于暴露于来自空间等离子体的高能离子。铁硫化物矿物硫铁矿（FeS）和磁黄铁矿（Fe 1 −xS）是重要的已知尘埃成分，但它们在尘埃空间环境中的空间辐射处理中发生结构变化（包括非晶化）的潜力尚未相对于硅酸盐进行实验评估。我们使用了透射电子显微镜（TEM）与原位离子辐照的能力，以精确地跟踪暴露于1.0 MeV的Kr++离子的硫铁矿和磁黄铁矿的结构变化，以优化从核弹性碰撞过程诱导非晶化的概率。 在1 × 1016 Kr++离子cm−2的实验实际离子剂量下，两种矿物都没有发现非晶化的迹象，表明两种结构都可以保持结晶状态，直到模拟的碰撞损伤水平至少为26个位移/原子。 这种行为与已知的一些最耐辐射的非金属相匹配，并且比富镁橄榄石和顽火辉石在相同辐照条件下变成无定形的水平高两个数量级。虽然磁黄铁矿在辐照过程中保留了短程结晶有序，但其较长范围的空位有序超结构在相当于橄榄石和顽火辉石变成无定形的损伤水平下被去除。这表明，足以使橄榄石和顽火辉石在星周和星际环境中非晶化的空间辐射条件将使共存的磁黄铁矿转变为无序的结构形式，从而改变磁黄铁矿的磁性和可能的其他性质，这些性质决定了磁黄铁矿在这些环境中的行为。
Abstract– Mineral grains that comprise dust particles in circumstellar, interstellar, and protostellar environments can potentially undergo amorphization and other solid‐state transformations from exposure to energetic ions from space plasmas. The Fe‐sulfide minerals troilite (FeS) and pyrrhotite (Fe1−xS) are important known dust components, but their potential to undergo structural changes, including amorphization, from space radiation processing in dusty space environments has not been experimentally evaluated relative to silicates. We used a transmission electron microscope (TEM) with capabilities for in situ ion irradiation to precisely follow structural changes in troilite and pyrrhotite exposed to 1.0 MeV Kr++ ions selected to optimize the probability of inducing amorphization from nuclear elastic collisional processes. No indication of amorphization was found in either mineral up to an experimentally practical ion dose of 1 × 1016 Kr++ ions cm−2, indicating that both structures can remain crystalline up to a modeled collisional damage level of at least 26 displacements‐per‐atom. This behavior matches that of some of the most radiation‐resistant nonmetallic phases known, and is two orders of magnitude higher than the levels at which Mg‐rich olivine and enstatite become amorphous under the same irradiation conditions. Although pyrrhotite retained short‐range crystalline order during irradiation, its longer range vacancy‐ordered superstructure is removed at modeled damage levels equivalent to those at which olivine and enstatite become amorphous. This suggests that space radiation conditions sufficient to amorphize olivine and enstatite in circumstellar and interstellar environments would convert coexisting pyrrhotite to its disordered structural form, thereby changing magnetic and possibly other properties that determine how pyrrhotite will behave in these environments.