Laboratory investigation of crystallisation in annealed amorphous MgSiO$\mathsf{_{3}}$
Laboratory investigation of crystallisation in annealed amorphous MgSiO$\mathsf{_{3}}$
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退火非晶 MgSiO$mathsf{_{3}}$ 结晶的实验室研究
DOI：
10.1051/0004-6361:20000576
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发表时间：
2001
影响因子：
6.5
通讯作者：
C. Tang
中科院分区：
文献类型：
--
作者：
S. P. Thompson;C. Tang
。原位高分辨率同步加速器 X 射线粉末 di(cid:11) 反应测量用于探测非晶 MgSiO 3 样品在退火过程中的结构变化。温度覆盖了天体物理上重要的 (cid:12) 范围 1000 K 至 1173 K，并且在退火之前样品显示出典型的非晶结构。 (cid:24)在1000K下退火2小时后，形成了与改性(cid:12)化的无定形组分共存的初始微晶。温度升高加上较长的退火时间不会对非晶成分产生进一步的变化，并且仅对结晶相的外观产生非常微小的变化。我们将其确定为结晶过程中的结构失速，并且可能是类似硅酸盐材料报道的光谱失速的根源。最终在 1173 K 下，经过 (cid:24) 79 小时的累积退火时间，非晶背景开始塌陷，同时进一步形成结晶特征。结构发展的停滞是因为结晶过程部分受到退火过程中非晶相的调节。在低端温度下，退火过程本身可能会强化非晶相，使其能够在相对较高的温度下存活。这一（cid：12）发现表明，一些较低温度的信息可能保存在某些最初在较低温度下退火的宇宙尘埃颗粒中。
. In situ high resolution synchrotron X-ray powder di(cid:11)raction measurements are used to probe the structural changes in a sample of amorphous MgSiO 3 during annealing. Temperatures cover the astrophysically signi(cid:12)cant range 1000 K to 1173 K and prior to annealing the sample showed typical amorphous structure. Following (cid:24) 2 hours annealing at 1000 K an initial crystallite had formed that was coexistent with a modi(cid:12)ed amorphous component. Increases in temperature coupled with long annealing times produced no further change to the amorphous component and only very minor changes in the appearance of the crystalline phase. This we identify as a structural stall in the crystallisation process and is likely to be the origin of the spectral stall reported for similar silicate materials. Finally at 1173 K, following a cumulative annealing time of (cid:24) 79 hours, the amorphous background began to collapse coinciding with the development of further crystalline features. The stall in structural development arises because the crystallisation process is in part regulated by the amorphous phase during annealing. At low-end temperatures it is likely that the annealing process itself strengthens the amorphous phase allowing it to survive up to relatively high temperatures. This (cid:12)nding suggests that some lower temperature information may be preserved in certain cosmic dust grains that were initially annealed at lower temperatures.