Development of a semi-continuous centrifugal process for classifying colloidal particles

近年来，基于亚微米颗粒的新型材料的开发取得了进一步的进展。然而，获得通常所需的窄粒度分布对于大多数方法是一个问题。考虑到中试或工业规模的生产，合成胶体的粒度分布通常太宽而不能用于尖端技术，例如可印刷电子产品、半导体抛光介质（CMP浆料）和用于癌症治疗的复合颗粒。因此，在随后的步骤中必须将窄馏分与主要的宽分布分离。这个过程的术语是分类。分级是通过去除细颗粒或粗颗粒来实现的。在中试规模中通过离心对颗粒进行连续或半连续分级显示出关于颗粒尺寸和颗粒与悬浮液周围液体的密度差异的某些限制。这些分离过程取决于大于1微米的颗粒尺寸和固体和液体之间至少两倍的密度差。亚微米颗粒的分类迄今仅限于实验室规模。在中试和工业规模中，选择性低的深床过滤器用于去除CPM浆料中的粗粒级分。深层过滤过程的优化是不可能的，因为决定性的物理学阻碍了选择性的增加。因此，该应用项目的目的是使用管式离心机研究纳米级的分级。固体和周围液体之间的密度差为100 kg/m³，切割尺寸为100 nm。对于颗粒和液体之间的密度差异较大，20 nm的切割尺寸似乎是可实现的。通过使用碳纤维转子和主动磁轴承，管式离心机产生高达160000 G的分类胶体颗粒。离心机是在当前的研究项目中构建的，需要针对预期应用进行修改。研究结果将描述各种颗粒系统的沉降行为与颗粒特性和工艺参数的关系。进一步的工作包是在离心机中用激光多普勒风速仪表征流型。该技术已用于管式离心机内流型的测量。研究结果已于近日公布。获得的流动特性知识将用于优化进气道几何形状。需要进一步测量以了解离心机进料系统附近的颗粒和流动通道。这对于实现预期的切割尺寸非常重要。此外，通过实验确定的流型可以验证将在应用项目中进行的模型计算。

Within the last years further progress was made in development of novel materials based on submicron particles. However, obtaining the commonly required narrow particle size distribution is a problem for most processes. With a view to production in pilot or industrial scale, particle size distributions of the synthesized colloids are often too broad to be used in cutting edge technology such as printable electronics, polishing media for semiconductors (CMP slurries) and composite particles used for cancer treatment. For this reason narrow fractions must be separated from the primarily broad distributions in subsequent steps. The term for this process is classification. Classification is either achieved by removing the fine or the coarse fraction.A continuous or semi-continuous classification of particles by centrifugation in pilot scale shows certain limitations concerning particle size and difference in density of the particles and the surrounding liquid of the suspension. Those separation processes depend on particle sizes larger than 1 µm and density differences between solid and liquid of at least a factor of two. The classification of submicron particles is so far limited to the laboratory scale. In pilot and industrial scale, deep bed filters that are low in selectivity are used to remove the coarse fraction in CPM slurries. An optimization of deep bed filtration process is not possible, because the determining physics impede an increase of selectivity. Thus, the aim of the applied project is the investigation of classification in the nanometre scale using a tubular bowl centrifuge.With a density difference between solid and the surrounding liquid of 100 kg/m³ a cut size of 100 nm is aspired. For higher differences in density between particles and liquid a cut size of 20 nm seems achievable. By using carbon fibre rotor and active magnetic bearings, the tubular bowl centrifuge generates up to 160000 G for classification of colloidal particles. The centrifuge is built in a current research project and needs to be modified for the intended application. The results of the investigations will describe the sedimentation behaviour of various particle systems in dependence of particle properties and process parameters.A further work package is the characterization of the flow pattern by Laser Doppler Anemometry in a centrifuge. This technique had been employed for measuring the flow pattern in a tubular bowl centrifuge. The results have been published recently. The gained knowledge of the flow characteristics will be used to optimize the inlet geometry. Further measurements are necessary to understand the particle and flow channelling close to the feeding system in the centrifuge. This is highly important to achieve the intended cut size.Furthermore the experimentally determined flow pattern enables the validation of the model calculations which will be carried out within the applied project.