Automated Filling of Dry Micron-Sized Particles into Micro Mold Pattern within Planar Substrates for the Fabrication of Powder-Based 3D Microstructures

Powder-based techniques are gaining increasing interest for the fabrication of microstructures on planar substrates. A typical approach comprises the filling of a mold pattern with micron-sized particles of the desired material, and their fixation there. Commonly powder-loaded pastes or inks are filled into the molds. To meet the smallest dimensions and highest filling factors, the utilization of dry powder as the raw material is more beneficial. However, an appropriate automated technique for filling a micro mold pattern with dry micron-sized particles is missing up to now. This paper presents a corresponding approach based on the superimposition of high- and low-frequency oscillations for particle mobilization. Rubber balls are utilized to achieve dense packing. For verification, micromagnets are created from 5 µm NdFeB powder on 8” Si substrates, using the novel automated mold filling technique, as well as an existing manual one. Subsequent atomic layer deposition is utilized to agglomerate the loose NdFeB particles into rigid microstructures. The magnetic properties and inner structure of the NdFeB micromagnets are investigated. It is shown that the novel automated technique outperforms the manual one in major terms.

Achieving Ultra-High Performance Concrete by Using Packing Models in Combination with Nanoadditives

This paper describes the packing models that are fundamental for the design of ultra-high-performance concrete (UHPC) and their evolution. They are divided into two large groups: continuous and discrete models. The latter are those that provide the best method for achieving an adequate simulation of the packing of the particles up to nanometric size. This includes the interaction among the particles by means of loosening and wall coefficients, allowing a simulation of the virtual and real compactness of such particles. In addition, a relationship between virtual and real compactness is obtained through the compaction index, which may simulate the energy of compaction so that the particles are placed in the mold. The use of last-generation additives allows such models to be implemented with water–cement (w/c) ratios close to 0.18. However, the premise of maximum packing as a basic pillar for the production of UHPC should not be the only one. The cement hydration process affected by nanoadditives and the ensuing effectiveness of the properties in both fresh and hardened states according to the respective percentages in the mixture should also be studied. The characterization tests of the aggregates and additions (dry and wet compactness, granulometry, density and absorption) have been carried out in order to implement them numerically in the polydisperse packing model to obtain the compactness of the mixture. Establishing fixed percentages of nanoadditives in the calculation of the mixture’s compactness. The adequate ratio and proportion of these additions can lead to better results even at lower levels of compactness. The compressive strength values obtained at seven days are directly proportional to the calculated compactness. However, at the age of 28 days, better results were obtained in mixes with lower cement contents, fewer additions and lower compactness. Thus, mixes with lower cement contents and additions (silica fume and limestone filler) with a compactness of φ = 0.775 reached 80.1 MPa of strength at 7 days, which is lower than mixes with higher cement contents and number of additions (SF, limestone filler and nanosilica), which achieved a compactness of φ = 0.789 and 93.7 MPa for compressive strength. However, at 28 days the result was reversed with compressive strengths of 124.6 and 121.7 MPa, respectively.

Pore Structure of Grain-Size Fractal Granular Material

Numerous studies have proven that natural particle-packed granular materials, such as soil and rock, are consistent with the grain-size fractal rule. The majority of existing studies have regarded these materials as ideal fractal structures, while few have viewed them as particle-packed materials to study the pore structure. In this study, theoretical analysis, the discrete element method, and digital image processing were used to explore the general rules of the pore structures of grain-size fractal granular materials. The relationship between the porosity and grain-size fractal dimension was determined based on bi-dispersed packing and the geometric packing theory. The pore structure of the grain-size fractal granular material was proven to differ from the ideal fractal structure, such as the Menger sponge. The empirical relationships among the box-counting dimension, lacunarity, succolarity, grain-size fractal dimension, and porosity were provided. A new segmentation method for the pore structure was proposed. Moreover, a general function of the pore size distribution was developed based on the segmentation results, which was verified by the soil-water characteristic curves from the experimental database.

Imaging microstructure of the barley rhizosphere: particle packing and root hair influences

Soil adjacent to roots has distinct structural and physical properties from bulk soil, affecting water and solute acquisition by plants. Detailed knowledge on how root activity and traits such as root hairs affect the three-dimensional pore structure at a fine scale is scarce and often contradictory. Roots of hairless barley (Hordeum vulgare L. cv Optic) mutant (NRH) and its wildtype (WT) parent were grown in tubes of sieved (<250 μm) sandy loam soil under two different water regimes. The tubes were scanned by synchrotron-based X-ray computed tomography to visualise pore structure at the soil-root interface. Pore volume fraction and pore size distribution were analysed vs distance within 1 mm of the root surface. Less dense packing of particles at the root surface was hypothesised to cause the observed increased pore volume fraction immediately next to the epidermis. The pore size distribution was narrower due to a decreased fraction of larger pores. There were no statistically significant differences in pore structure between genotypes or moisture conditions. A model is proposed that describes the variation in porosity near roots taking into account soil compaction and the surface effect at the root surface.