The pursuit of homogenous powder mixtures is of interest to an extremely diverse range of market sectors, from food and beverages to pharmaceuticals. Significant research and development (R&D) efforts are expended trying to blend two or more individual powder materials into a stable, homogenous mixture for intermediate or end-use. These early stages of development are characterized by several distinct forms of materials characterization (content uniformity, particle characterization, etc.); an approach that can permeate every stage of the manufacturing cycle.
Even when an appropriate mixture has been achieved, segregation testing must be conducted to interrogate the stability of solid-phase mixtures in real-world conditions. These include processing, storage, and use environments where disturbing forces can cause a homogenous mixture to separate. Although segregation mechanics are extremely varied, they rarely result in total separation and are instead characterized by the formation of local heterogeneities within the bulk mixture. The consequences of this largely depend on the area of the intended application.
Segregation Testing: Materials Characterization & Process Optimization
There are two primary purposes for gathering segregation data from powder mixtures. Engineers typically wish to either:
- A) Improve product design by minimizing the extent and impact of segregation, OR;
- B) Improve the processing environment to limit the effect of segregation on key components like feeds and hoppers.
Fortunately, each of these areas of study is typically concerned with the same key performance indicators (KPIs) with respect to the magnitude and method of segregation in bulk powders. While there are many influencing factors, five primary methods of separation have been identified in typical handling systems: air entrainment, angle of repose differences, impact fluidization, percolation, and sifting.
- Air entrainment refers to the separation of fines from the bulk material due to air currents, i.e. from free fall in processing equipment.
- Angle of repose differences occur due to differences in flow characteristics between components, causing a heterogeneous distribution across the surface of a pile.
- Impact fluidization generally occurs in extremely fine mixtures where trapped air within the bulk mixture causes the material to adopt fluidic properties. Larger particles can easily penetrate this finer layer, causing the bulk material to separate into a top-to-bottom distribution of fine-to-coarse particles.
- Percolation is similar to impact fluidization, in that the mixture separates heterogeneously from top-to-bottom, except it occurs due to the loss of entrained air.
- Sifting is a common segregation mechanic that causes fine particles to separate from comparatively coarser ones due to inter-particle motion.
Many materials characterization instruments intended for use with particles are limited by their testing methodologies, using either a rotating drum to measure the angle of repose, a fluidized bed to assess various forms of fluidization, or some form of shaker to address the impact of general agitation. Although this can provide accurate insights into the powder properties and inform a range of materials characterization techniques, it does not provide the most accurate data with regards to process optimization.
A solution to this is the SPECTester Innovative Segregation Tester from Particulate Systems.
Materials Characterization with Particulate Systems
The SPECTester is a unique materials characterization tool designed specifically for the identification of primary and secondary segregation mechanisms, with accurate simulation of processing conditions. It boasts full-automation of operations and 50 distinct segregation sample points across a single sample bed, offering robust insights into the behavior of complex powder mixtures in response to a range of distorting phenomena. Particulate System’s SPECTester is ideal for a range of application areas, including materials characterization for both product and production optimization, streamlining testing workflows for actionable insights as soon as possible.
Particulate Systems was established on the core ideologies of innovation and responsiveness, providing integrated solutions for materials characterization in facilities of all scales. If you have found this post interesting and would like to learn more about the distinct segregation mechanisms affecting bulk powders, read our previous blog post:Posted on