Assessing Flowability of Cohesive Powders from a Small Sample Quantity

精细和粘性粉末的加工是非常困难的，并且经常受到粉末流动行为不一致的影响，这对设备的可靠性和生产率产生不利影响。制药、精细化工和核工业就是很好的例子，在这些行业中，少量粘性粉末的定量和分散在技术上非常具有挑战性。例如，对于通过肺的药物递送，干粉吸入器的功能性强烈依赖于弱压实的散装粉末的流动性。目前用于评估粉末流动行为的测试方法（无侧限压缩和剪切单元测试）需要相对大量（至少100 g）的粉末。这对于诸如核工业和制药工业是不期望的，因为前者的电离辐射和后者的毒性、药物成本以及在开发的早期阶段缺乏可用性。此外，传统的试验方法不适用于测试非常弱的压坯，并且填料可能不同于常用的方法，如无侧限压缩和剪切单元。因此，必须在其自身容器中评估样品的流动性。该研究项目旨在通过压痕探针法评估细粘性粉末在小尺度（通常为几立方毫米）和非常低的载荷下的变形和流动行为的分析。提出了一个综合的方法来实现这一目标，其中包括实验工作，以分析单个颗粒的机械性能和散装流动行为和模拟工作，将散装行为与初级颗粒的性能。所描述的过程将建立受到压缩的颗粒集合体的微观行为和宏观行为之间的联系，并将阐明颗粒形成强压块的情况。特别是交付的是：-粉末流动功能之间的相关性，基于无侧限屈服应力，和几立方毫米的样品的压痕特性;-一个验证的测试方法，用于测量大量的粘性粉末的整体屈服应力;-在低负载下的粉末变形的理解。

Processing of fine and cohesive powders is very difficult and often marred by inconsistencies in powder flow behaviour which adversely affects plant reliability and productivity. Good examples are in pharmaceutical, fine chemicals and nuclear industries, where dosing and dispersion of small quantities of cohesive powders is technologically very challenging. For instance for drug delivery through lungs the functionality of dry powder inhalers is strongly dependant on flowability of weakly compacted bulk powders. Current test methods for assessing the flow behaviour of powders (unconfined compression and shear cell testing) require a relatively large amount (at least 100 g) of powders. This is undesirable for industries such as nuclear and pharmaceutical due to ionising radiation for the former and toxicity, cost of drugs and lack of availability at the early stages of development for the latter. Furthermore the traditional test methods are not suitable for testing very weak compacts and the packing may be different from that used in the common methods such as unconfined compression and shear cell. Therefore the flowability of the sample has to be assessed in its own container. This research project is formulated to evaluate the analysis of the deformation and flow behaviour of fine cohesive powders at small scales (typically a few cubic mm) and at very low loads by the indentation probe method. An integrated approach is proposed to achieve the goal, which includes experimental work to analyse the mechanical properties of the single particles and bulk flow behaviour and simulation work to relate the bulk behaviour to the properties of primary particles. The described procedure will establish a link between the microscopic and macroscopic behaviour of particle assemblies subjected to compression and will elucidate the circumstances under which the particles form a strong compact. In particular the deliverables are:-a correlation between powder flow function, based on the unconfined yield stress, and indentation characteristics for samples of a few cubic mm;-a validated test methodology for measurement of the bulk yield stress of small quantities of cohesive powders;-an understanding of powder deformation at low loads.