Powder Characterization Techniques Research Articles

A Comprehensive Review of the Rheological Properties of Powders in Pharmaceuticals

The perpetual significance of the pharmaceutical industry in society necessitates ongoing research efforts to enhance the efficacy of its manufacturing processes. Given that drug product manufacturing typically involves powder processing, a thorough understanding of powder characterization is needed for optimal process performance. Powder rheology is commonly examined in pharmaceutical manufacturing to elucidate the relationship between powder properties and the performance of pharmaceutical processes. This paper provides a brief discussion of recent literature regarding the various powder properties and characterization techniques encompassed in powder rheology. The powder properties are categorized into particle size, particle morphology, friability, electrostatics, permeability, wettability, cohesion, bulk density, and agglomeration sections. A distinct focus is placed on the segment about powder wettability. This review informs readers about the fundamental properties of powders known to influence pharmaceutical processes. It discusses the interrelationships among these properties, powder characterization techniques, and ideal states of powder properties that lead to optimal process performance.

Powder degradation as a consequence of laser interaction: A study of SS 316L powder reuse on the laser directed energy deposition process

The feedstock capture efficiency on powder laser directed energy deposition (L-DED) is becoming a big challenge in the industrial use of the L-DED process for the manufacturing of large-scale AM parts. The powder capture efficiency is dependent on process optimization and the toolpath. The current literature presents a vast range of usual powder efficiency, between 3% and 32% and in some specific cases exceeding 90%. In L-DED, the powder-gas jet stream interacts with the laser beam adding material locally onto the substrate. Part of this material is captured by the melt pool. The not captured material that is affected by the laser beam suffers degradation. In the literature, there is a lack of studies related to powder reuse in the L-DED process. This paper presents a comprehensive study on the consequence of laser interaction with SS 316L metal powder particles during the L-DED process using a range of different powder characterization techniques to assess the powder morphology, size distribution, chemical composition, followability, and density. The study was conducted within eight powder reuse cycles, without adding virgin material to the powder batch. Reduction of particle size distribution range, increase in circularity, and improvement in the powder flowability were identified as consequences of powder reuse. The result of laser interaction with particles was further explored by scanning electron microscopy, presenting the continuous modification of the particles across the eight reuse cycles. The oxygen content on the particles was also measured to access the O2 pick-up as a consequence of particle heating.

Effect of particle size distribution on the flowability of plasma atomized Ti-6Al-4V powders

The flowability of metal powders is critical to many additive manufacturing (AM) processes, particularly for laser or electron-beam powder bed fusion. Many poewder features may simultaneously influence its powder flow behavior, yet how particle size distribution (PSD) individually affects its flowability has not been comprehensively evaluated. The plasma atomization technique allows the production of high-quality spherical metal powders with various PSDs. The recent development of powder characterization techniques offers an opportunity to accurately measure a variety of powder flow properties, including Hausner ratio, Hall flow rate, rheology properties. In this study, we measured the flow properties for six Ti-6Al-4V powders with distinct PSDs. Our results show that the PSD plays a significant role in powder flowability: (1) Either a larger mean particle size or a narrower PSD enhances the powder flowability; The multimodal distribution of PSD is beneficial for the powder bulk flow properties. (2) Either a larger particle mean size or a narrower PSD enhances the powder rheology. (3) Powder dynamic flowing behavior is only influenced by the powder mean size, but not affected by PSD. Powder dynamic flowability improves with increasing particle size. Furthermore, we propose a general formula that can be used to qualitatively estimate the average score of the flowability for metal powders based on the three types of indicators. This study could provide a general guide to predict metal powder flowability based on PSD.

Examination of the evolution of iron oxide nanoparticles in flame spray pyrolysis by tailored in situ particle sampling techniques

In this report, a flame spray pyrolysis setup has been examined with various in situ extraction methods of particle samples along the flame axis. First, two precursor formulations leading to the formation of iron oxide nanoparticles were used in a standardized SpraySyn burner system, and the final particle outcome was characterized by a broad range of established powder characterization techniques (TEM/HRTEM, SAXS, XRD, BET). The characterization of the powder products evidenced that mostly homogeneous gas-to-particle conversion takes place when applying an acidic precursor solution, whereas the absence of the acid leads to a dominant droplet-to-particle pathway. Our study indicates that a droplet-to-particle-pathway could be present even when processing the acidic formulation. However, even if a secondary pathway might take place in this case as well, it is not dominant and nearly negligible. Subsequently, the in situ particle structure evolution was investigated for the dominant gas-to-particle pathway, and particles were extracted along the flame axis for online SMPS and offline TEM/HRTEM analysis. Due to the highly reactive conditions within the flame (high temperatures, turbulent flow field, high particle number concentrations), the extraction of representative samples from spray flames is challenging. In order to handle the reactive conditions, two extraction techniques were tailored in this report. To extract an aerosol sample within the flame for SMPS measurement, a Hole in a Tube probe was adjusted. Thus, the mobility particle diameter as well as the corresponding distribution widths were obtained at different heights above the burner along the flame axis. For TEM/HRTEM image analysis, particle samples were collected thermophoretically by means of a tailored shutter system. Since all sampling grids were protected until reaching the flame axis and due to the low sampling time, momentary captures of local particle structures could be extracted precisely. The particle morphologies have clearly shown an evolution from spherical and paired particles in the flame center to fractal and compact agglomerates at later synthesis stages.

Powder Characterization Techniques

Abstract Knowledge of the characteristics of powders is of paramount importance for the successful development and application of powder metallurgy and particulate materials. Early characterization techniques were related to press and sinter powder metallurgy, dealing with the relatively coarser powders and with the analysis of individual as well as mass of powders. These analyses include structure, chemistry, morphology, size, shape, their distribution, different densities, flow, porosity, compressibility, friction, shear, residual stress, and so on to obtain a defect-free product. The advent of nanopowders and nanotechnology, metal injection molding, and more recent additive manufacturing has to deal with finer powders and different processing steps, which has resulted in the advancement of traditional powder characterization techniques to the next level, evolving newer and more innovative characterization techniques. Consequently, techniques such as x-ray photoelectron spectroscopy, scanning electron microscopy, laser light diffraction, x-ray computed tomography scan, atomic force microscopy, differential thermal analysis, etc., have been used with emphasis on powder cleanliness and internal particle porosity. The widely used industrial additive manufacturing process uses powder bed fusion that bonds successive layers of powders to facilitate the fabrication of parts with complex geometries. Thus, this article also explores the emerging trends in dynamic powder testing using a powder rheometer to measure dynamic flowability from measurement of axial and rotational forces acting on the rotating blade and the study of spreadability and flowability of powders by rotating drum instruments. A judicious selection of relevant and appropriate powder characterization techniques will ensure predictable powder behavior during the manufacturing process, resulting in consistent and reliable products.

Material-Sparing and Expedited Development of a Tablet Formulation of Carbamazepine Glutaric Acid Cocrystal- a QbD Approach.

To efficiently develop a tablet formulation of carbamazepine using a soluble cocrystal with excess coformer to maintain phase stability during dissolution. The carbamazepine - glutaric acid cocrystal (CBZ-GLA, 1:1) and excess glutaric acid (GLA) were mixed with suitable tablet excipients, which were selected to address powder flowability and tabletability deficiencies specifically. Tablet friability and dissolution profiles were evaluated to guide formulation optimization. Dry granules were prepared by milling simulated ribbons. A binary blend of CBZ-GLA and GLA had poor flowability and marginal tabletability. Therefore, silica coated Avicel PH-102 (sMCC) was applied as a binder to improve the flow property and tabletability. A formulation consisting of sMCC, CBZ-GLA, and GLA exhibited good manufacturability but did not show improved dissolution because of rapid precipitation of CBZ dihydrate when CBZ-GLA came in contact with water. Dry granulation of CBZ-GLA and GLA dramatically improved dissolution profile due to the intimate contact between CBZ-GLA and GLA. Such cocrystal - coformer granules also led to much improved tablet manufacturability and dissolution. The successful tablet development of CBZ-GLA, using < 3 g of the cocrystal in <3 weeks, demonstrates an efficient workflow for tablet formulation development based on material-sparing and predictive powder characterization techniques. This workflow is useful for early tablet development using enabling solid form, such as cocrystal, when only a small amount of material is available.

Advanced Powder Characterization for Additive Manufacturing

Abstract As powder-based additive manufacturing (AM) processes continue to mature, reliable powder characterization techniques will be key to optimizing both AM processes and final part performance. This article describes advanced metals for assessing powder properties and their influence on AM processing and part performance.

Characteristics of Inconel Powders for Powder-Bed Additive Manufacturing

Abstract In this study, the flow characteristics and behaviors of virgin and recycled Inconel powder for powder-bed additive manufacturing (AM) were studied using different powder characterization techniques. The results revealed that the particle size distribution (PSD) for the selective laser melting (SLM) process is typically in the range from 15 μm to 63 μm. The flow rate of virgin Inconel powder is around 28 s·(50 g)−1. In addition, the packing density was found to be 60%. The rheological test results indicate that the virgin powder has reasonably good flowability compared with the recycled powder. The inter-relation between the powder characteristics is discussed herein. A propeller was successfully printed using the powder. The results suggest that Inconel powder is suitable for AM and can be a good reference for researchers who attempt to produce AM powders.

Synthesis and characterization of lead-free piezoelectric (K0.50Na0.50)NbO3 powder produced at lower calcination temperatures: A comparative study with a calcination temperature of 850 °C

To prevent the evaporation of alkali elements during the calcination of the lead-free piezoelectric K0.50Na0.50NbO3 (KNN), lower temperatures for the solid-state synthesis of the KNN from a mixture of Na2CO3, K2CO3 and Nb2O5 were investigated with a variety of powder-characterization techniques. The collected data suggested 550°C as a possible low calcination temperature, as well as being sufficiently high for a completed synthesis of the KNN. The XRD and TEM analyses of double-calcined KNN powder at 550°C revealed nanocrystalline, cube-shaped particles with a perovskite structure, but without noticeable unreacted precursors or secondary phases. Our investigations revealed that the morphology of the calcined powders underwent a dramatic change from small, differently shaped particles at 600°C/6h, to fully rounded, large, spherical agglomerates produced at 1000°C/6h. To explain this behavior, a mechanism involving the formation of a liquid phase during the reaction of the alkali elements with the moisture and CO2 in the atmosphere is proposed.

In-process sensing in selective laser melting (SLM) additive manufacturing

Additive manufacturing and specifically metal selective laser melting (SLM) processes are rapidly being industrialized. In order for this technology to see more widespread use as a production modality, especially in heavily regulated industries such as aerospace and medical device manufacturing, there is a need for robust process monitoring and control capabilities to be developed that reduce process variation and ensure quality. The current state of the art of such process monitoring technology is reviewed in this paper. The SLM process itself presents significant challenges as over 50 different process input variables impact the characteristics of the finished part. Understanding the impact of feed powder characteristics remains a challenge. Though many powder characterization techniques have been developed, there is a need for standardization of methods most relevant to additive manufacturing. In-process sensing technologies have primarily focused on monitoring melt pool signatures, either from a Lagrangian reference frame that follows the focal point of the laser or from a fixed Eulerian reference frame. Correlations between process measurements, process parameter settings, and quality metrics to date have been primarily qualitative. Some simple, first-generation process control strategies have also been demonstrated based on these measures. There remains a need for connecting process measurements to process models to enable robust model-based control.

Multi-faceted characterization of pharmaceutical powders to discern the influence of surface modification

Abstract The present work is a comprehensive investigation of the flow, packing, and aeratibility behavior and discerning the rank order of several Active Pharmaceutical Ingredients (API), with or without surface modification, as well as excipients with different particle sizes and shapes. Surface modification of the API powders (various size grades of acetaminophen, ascorbic acid and ibuprofen) was conducted in a magnetically assisted impaction coater (MAIC), a well-established material sparing device. Powder characterization was done using various conventional and novel powder characterization techniques to measure properties such as, angle of repose, flow index, aerated, tapped and conditioned bulk densities, Housner ratio, Carr index, flow function coefficient (FFC), cohesivity and aeratibility. The comparative results show that surface modification improves flow, packing and aeratibility of powders with respect to corresponding as received powders, and in many cases, dry coated API powders exhibit properties as good as or better than similar sized excipients. The measured properties from different instruments were plotted through several illustrative phase maps with intent to develop a better visualization of the property improvements via dry coating. It was seen in the phase map of FFC vs. conditioned bulk density that it was easy to visualize a clear change in flow regimes after surface modification. For example, surface modified fine API powders show a shift from highly cohesive region (FFC 10) along with an increase in conditioned bulk density ( 0.5 g/ml). The use of the proposed phase map in developing manufacturing feasibility guidelines is also proposed.

Flow properties of fine powders in powder coating

Three types of nanoparticles and their combinations were blended into a fine powder, which has been used in the powder coating industry. To study their effects on flow properties, the modified powder samples were characterized using a variety of techniques that tested the powder under different powder states ranging from dynamic to static. It was found that all three nanoparticles improved the flow properties of the powder to some degree, though the amounts of the nanoparticles needed were different depending on their physical properties. Secondly, inconsistency among these powder characterization techniques was also found. This is attributed to the different states of the powder samples during a measurement including dynamic, dynamic-static and static states. It was confirmed that characterization techniques which test the flow properties of a powder under all three states are needed to fully describe the flow properties of the powder. Finally, the effects of combinations of nanoparticles were explored, and it was found that combinations of nanoparticles can intensify, weaken or combine the effects of their component nanoparticles. The effects of nanoparticle combinations are not a simple summation of the effects of their component nanoparticles.