Mechanisms of ultrasonic de-agglomeration of oxides through in-situ high-speed observations and acoustic measurements.
Mechanisms of ultrasonic de-agglomeration of oxides through in-situ high-speed observations and acoustic measurements.
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DOI：
10.1016/j.ultsonch.2021.105792
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发表时间：
2021-11
影响因子：
8.4
通讯作者：
Tzanakis I
中科院分区：
文献类型：
--
作者：
Priyadarshi A;Khavari M;Subroto T;Prentice P;Pericleous K;Eskin D;Durodola J;Tzanakis I
高速成像捕捉到氧化物聚集体的解聚和分散。团聚体的本体和表面都发生了解聚。漂浮的微泡簇无人机产生松散附聚物的精细悬浮液。超声毛细效应促进了颗粒内部的解聚。次谐波和低次超谐波气泡辐射导致氧化层破裂。氧化物的超声解聚和分散对于一系列应用是重要的。特别是在液态金属中，这是制备用微米和纳米尺寸颗粒增强的金属基复合材料的方法之一。然而，通过相关的机制发生的解团聚，只是概念化的理论，尚未与实验观察验证。本文首次利用高速成像技术原位观察了超声空化对SiO2和MgO团聚体（通常在轻质合金中作为增强体）的影响，这些团聚体的单个颗粒尺寸在0.5 ~ 10 μm之间。由于液态金属的不透明性，在去离子水中进行了去团聚成像实验，其中以高达50 kfps的帧速率捕获序列。现场观察还伴随着同步声学测量使用先进的校准的空化计，揭示振荡微泡氧化物解聚所产生的压力振幅的影响。结果表明，超声诱导的微泡团簇的混沌脉动，是主要负责的氧化物团聚体的破碎和分散。观察到这种振荡空化簇捕获漂浮的团聚物，导致其立即崩解。氧化物的解聚发生在聚集体的表面和内部。微泡团簇在驱动频率的次谐波、1次谐波和低次超谐波下以相关发射频率振荡被认为是团聚体破裂的原因。
High-speed imaging captured de-agglomeration and dispersion of oxide aggregates. De-agglomeration occurred from both bulk and surface of the aggregate. Floating microbubble cluster drones produced fine suspension of loose agglomerates. Ultrasonic capillary effect promoted de-agglomeration of particles from within. Subharmonic and low order ultra-harmonic bubble emissions induced oxide breakage. Ultrasonic de-agglomeration and dispersion of oxides is important for a range of applications. In particular, in liquid metal, this is one of the ways to produce metal-matrix composites reinforced with micron and nano sized particles. The associated mechanism through which the de-agglomeration occurs has, however, only been conceptualized theoretically and not yet been validated with experimental observations. In this paper, the influence of ultrasonic cavitation on SiO2 and MgO agglomerates (commonly found in lightweight alloys as reinforcements) with individual particle sizes ranging between 0.5 and 10 μm was observed for the first time in-situ using high-speed imaging. Owing to the opacity of liquid metals, a de-agglomeration imaging experiment was carried out in de-ionised water with sequences captured at frame rates up to 50 kfps. In-situ observations were further accompanied by synchronised acoustic measurements using an advanced calibrated cavitometer, to reveal the effect of pressure amplitude arising from oscillating microbubbles on oxide de-agglomeration. Results showed that ultrasound-induced microbubble clusters pulsating chaotically, were predominantly responsible for the breakage and dispersion of oxide agglomerates. Such oscillating cavitation clusters were seen to capture the floating agglomerates resulting in their immediate disintegration. De-agglomeration of oxides occurred from both the surface and within the bulk of the aggregate. Microbubble clusters oscillating with associated emission frequencies at the subharmonic, 1st harmonic and low order ultra-harmonics of the driving frequency were deemed responsible for the breakage of the agglomerates.
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