Aggregation is a common process occurring in many diverse particulate gas mixtures (e.g. those derived from explosive volcanic eruptions, meteorite impact events, and fluid bed processing). It results from the collision and sticking of particles suspended in turbulent gas/air. To date, there is no generalized model of the underlying physical processes. Here, we investigate aggregates from 18 natural deposits (16 volcanic deposits and two meteorite impact deposits) as well as aggregates produced experimentally via fluidized bed techniques. All aggregates were analyzed for their size, internal structuring, and constituent particle size distribution. Commonalities and differences between the aggregate types are then used to infer salient features of the aggregation process. Average core to rim ratios of internally structured aggregates (accretionary lapilli) is found to be similar for artificial and volcanic aggregates but up to an order of magnitude different than impact-related aggregates. Rim structures of artificial and volcanic aggregates appear to be physically similar (single, sub-spherical, regularly-shaped rims) whereas impact-related aggregates more often show multiple or irregularly shaped rims. The particle size distributions (PSDs) of all three aggregate types are similar (< 200 μm). This proves that in all three environments, aggregation occurs under broadly similar conditions despite the significant differences in source conditions (particle volume fraction, particle size distribution, particle composition, temperature), residence times, plume conditions (e.g., humidity and temperature), and dynamics of fallout and deposition. Impact-generated and volcanic aggregates share many similarities, and in some cases may be indistinguishable without their stratigraphic context.

中文翻译：

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富颗粒环境中的聚集：火山喷发、陨石撞击和流化床处理实例的结构研究

聚集是发生在许多不同颗粒气体混合物中的常见过程（例如那些源自爆炸性火山喷发、陨石撞击事件和流化床处理的气体）。它是悬浮在湍流气体/空气中的颗粒碰撞和粘附的结果。迄今为止，还没有基本物理过程的通用模型。在这里，我们研究了来自 18 个天然沉积物（16 个火山沉积物和两个陨石撞击沉积物）的骨料以及通过流化床技术实验生产的骨料。分析了所有聚集体的尺寸、内部结构和组成粒度分布。然后使用聚合类型之间的共性和差异来推断聚合过程的显着特征。发现内部结构聚集体（增生性火山岩）的平均核心与边缘比率对于人工和火山聚集体是相似的，但与撞击相关的聚集体相差一个数量级。人造和火山聚集体的边缘结构似乎在物理上相似（单个、亚球形、规则形状的边缘），而与撞击相关的聚集体更常显示多个或不规则形状的边缘。所有三种骨料类型的粒度分布 (PSD) 都相似（< 200 μm）。这证明在所有三种环境中，尽管源条件（颗粒体积分数、粒度分布、颗粒组成、温度）、停留时间、羽流条件（例如，湿度和温度）存在显着差异，但在大致相似的条件下发生聚集，以及沉降和沉积的动力学。撞击生成的和火山的聚集体有许多相似之处，在某些情况下，如果没有它们的地层背景，可能无法区分。