Spherical Pores Research Articles

The role of defects and characterisation of tensile behaviour of EBM Additive manufactured Ti-6Al-4V: An experimental study at elevated temperature

The use of the Electron Beam Melting (EBM) Additive Manufacturing (AM) process to fabricate parts for applications which require strength and reliability is limited. EBM parts suffer from manufacturing defects and poor surface finish, and its strength properties can be dependent on strain rates and temperature. In this paper, the effects of parameters such as the strain rate, temperature, surface finish and build orientation together with the role of defects on tensile properties of EBM Ti-6Al-4V alloy have been studied and discussed. Due to reduced material density and multiplication rate of dislocations, a significant decrease in material tensile strength but an increase in material ductility was observed for tests on machined specimens at higher temperatures. Surface nucleating micro-cracks (poor surface finish) and inherent internal defects caused a reduction in tensile strength and material ductility for the as-built specimens. Coalescence of small size spherical pores and the presence of large voids have a direct deleterious effect on the ductility of Ti-6Al-4V alloy. The orientations of voids, difference in thermal history resulting into different microstructures, presence of grain boundary α and alignment of prior columnar β grains with respect to the loading direction for vertical and horizontal built specimens are the reasons for observed anisotropy in material strength of EBM Ti-6Al-4V alloy. The interaction effects of different parameters are also discussed, and it is suggested that these parameters should be optimised, in addition to the process parameters, to make AM parts using the EBM process which can reliably and safely be used for load bearing applications.

Tailored macro-pores during the formation of C/C-SiC via liquid phase pyrolysis

The synthesis of C/C-SiC via liquid silicon infiltration (LSI) with thermoplastic carbon precursors can lead to the formation of macropores in the C/C state. The macro-pore pattern formation can be controlled and used as a new level in microstructure for ceramic matrix composites. The pore formation occurs in the CFRP state with the remelting of the thermoplastic matrix and can be fixed to the C/C state after liquid phase pyrolysis. The macro-pores are primarily induced by a non-linear elastic recovery of the fiber preform and not via gas formation and release during pyrolysis. The formation of the macroporosity is described and explained. These pores can be tailored by process control in size and shape. The pore shapes can vary from isolated spherical pores to an interconnected tube like macro-pore network. The relationship between starting setting variables of the fiber preform, the process conditions, and the resulting structure are discussed.

Properties of Tool Steels Printed by Directed Energy Deposition Process on S45C Base Metal.

We present a fundamental study on the development of trimming dies at room temperature for the hot-stamping process using directed energy deposition. Specimens of G and F materials were fabricated by machining 3D-printed blocks. The hardness of G-layered specimens was slightly higher than that of F-layered specimens, reaching approximately 700 HV at the surface. The G-layered specimens consisted of columnar and equiaxed dendrites, whereas the F-layered specimens mainly consisted of equiaxed dendrites. Spherical pores were observed inside the layered cross section, whereas relatively large irregular-shaped cavities were observed in layered boundaries. The tensile strengths of the G-layered and F-layered specimens were approximately 1800 and 1650 MPa, respectively. During bonding strength tests on an area bonded with S45C base metal, a fracture occurred in one case because of the lack of fusion at the boundary, and the F-layered specimens showed a lower strength than the G-layered ones. During wear tests on a quenched 1.5 GPa-grade aluminized steel plate, the F-layered specimens showed lower wear loss. However, the G-layered specimens showed better wear resistance during wear tests on a 1.5 GPa-grade electrogalvanized steel plate. These findings serve as fundamental data for additive manufacturing processes using tool steels of high-strength materials with high melting points.

Mathematical Modeling for Losses in Optical Waveguides With Porous Silica Cladding

This paper presents a model to calculate the combined surface and volume scattering losses for optical waveguides containing porous silica materials. The simulation results agree with the published experimental loss data. The model for volume scattering loss considers the primary factors that affect the volume scattering including porosity, volume of pores and scattering cross section. The criteria of Rayleigh scattering was applied to either cylindrical or spherical pores to find the scattering cross section. Surface scattering loss was calculated using Tien’s model and the scattering models were applied to optical waveguides reported in previous publications. A good agreement between the experimental results and the models has been demonstrated. The ratio between calculated and experimental results were in the range of (0.9-1). Therefore, these models can be used to calculate scattering losses in optical waveguides including ones with porous silica claddings. Moreover, the scattering models in conjunction with ModeSolver MATLAB simulations have been applied to optical waveguide sensors with porous silica claddings for the first time to validate the possibility of designing LEAC sensors with porous silica claddings.

Influence of wet foam stability on the microstructure of ceramic shell foams

In this study, recycled ceramic shell particles from the mold used in precision casting, which consists of coating a wax model with several layers (shell) of mullite and zirconia particles of different sizes, were used as raw material to prepare stable wet-foams by direct foaming and gelcasting using ovalbumin. The control of suspension parameters, such as pH, dispersant concentration, solids concentration and stirring velocity, can influence the foam stability against destabilization mechanisms (such as drainage, coalescence, and Ostwald ripening), optimizing the final properties of the cellular ceramic structures. The rheological behavior of suspensions and the gel point temperature of foams was also evaluated. The evolution of the bubbles-sizes (as a function of time) into the wet foam structure was analyzed by Axio Vision LE and ImageJ software. The fired ceramic shell foam (1550 ​°C, 2 ​°C/min, for 2 ​h) exhibited porosities higher than 80%, characterized by a highly interconnected network of spherical pores, with sizes ranging from 518 ​± ​29 to 1088 ​± ​103 ​μm and compressive strength of 0.9 ​± ​0.2 ​MPa. The morphological features and mechanical strength of the obtained foam indicating the possibility that it could be employed as low-cost replacement for radiant porous burners applications.

Fatigue endurance limit and crack front evolution in metallic glass

Fatigue endurance limit is a threshold stress-amplitude under which a solid subjected to a cyclic loading can sustain infinite life. Such a limit has been confirmed in ferrous materials but remains controversial in many advanced new materials, including bulk metallic glasses with superb strength. By using a combination of ultrasonic fatigue (USF) test and conventional fatigue test, we obtain the stress amplitude vs. loading cycle curve of the Vitreloy 1TM metallic glass, with loading cycles up to 109. There is a clear fatigue endurance limit (FEL) which is about 320 MPa, and is 17% of the strength of Vitreloy 1TM. The residual strength of survivals after 109 cycles is nearly the same as those of intact samples. We demonstrate that all fatigue cracks initiate from spherical pores which are inevitable and intrinsic amid casting and fast cooling, and the fatigue crack front resembles an ellipse arc till final rapid rapture of all tested samples. The size and position of a pore can be utilized to extract the fatigue initiation threshold K0th, and the elliptical fatigue crack front is used to obtain the mode I fracture toughness KIC, which are K0th=2.0±0.5MPam and KIC=18-20MPam for Vitreloy 1TM, respectively. The fatigue endurance limit and its intrinsic origin of Vitreloy 1TM pave the way to understand fatigue in other metallic glasses.

Hydro-mechanical coupling in porous rocks: hidden dependences to the microstructure?

SUMMARY While hydro-mechanical coupling in rocks is generally well understood, exotic rock poroelastic responses—such as unexpected dependence to fluid diffusion time and low skeleton moduli—have been reported. Hydro-mechanical coupling, or poroelasticity, explains how fluid-saturated rocks respond to either confining or fluid pressure variations. This coupling is usually inferred from the apparent mechanical and hydraulic properties: mechanical properties determine the strain level experienced by the rock when submitted to pressures at a timescale when fluid pressure is equilibrated, which is in turn ruled by hydraulic properties. However, the coupling between properties might not always be straightforward, particularly for rocks in which two distinct families of pore types coexist: spherical pores and cracks. Comparing it with reported laboratory data sets on pressure-dependent hydraulic and elastic properties in sandstones of different porosity confirms that the well-known simple concepts of networks in parallel apply and yield opposite dependencies for the two properties on the two pore families. Because hydro-mechanical coupling implies that the two properties—that depend differently on the pore families—will be interdependent, we further apply the same concept of parallel network. It yields that, although under apparent drained conditions, typical poroelasticity experiments could underestimate the rock compressibility ${C_{\mathrm{ bp}}}$, measured as a response to fluid pressure variation, and underestimate the related skeleton (or unjacketed) bulk modulus ${K_\mathrm{ s}} = \ 1/{C_\mathrm{ s}}$.

Magneto-Seebeck and Nernst effects in porous semiconductors with hierarchically distributed nano-to micro-scale pores

The objective of this work is to study the magneto-Seebeck and transverse Nernst-Ettingshausen effects in semiconductors with spherical hollow pores of varying diameter from micrometers down to nanometers. The change in the magneto-Seebeck and Nernst coefficients due to the porosity is examined using a model based on the Gamma distribution of the pore sizes. Sound analytical expressions are found for the coefficients under both isothermal and adiabatic conditions in the presence of weak and strong non-quantizing magnetic fields. It is shown that the porosity leads to the decrease in the magneto-Seebeck coefficient in absolute value as compared with bulk material in both weak and strong fields. In contrast to that, the Nernst coefficient increases linearly with increasing porosity in strong fields while decreases by hyperbolic law in weak fields. The change in the coefficients is the greater the less is the average pore diameter.

Polymer brushes in pores by ATRP: Monte Carlo simulations

Growth and properties of polymer brushes anchored to the surface of cylindrical and spherical pores were studied using Monte Carlo computer simulations. Grafting density of studied dense brushes was higher than the polymer coil overlap density. The properties of brushes were “realistic” i.e. their dispersity depended on synthetic conditions such as the polymerization rate and the pore radius. The effect of surface curvature on properties of the brushes was analyzed. Brush relaxation was studied to determine true equilibrium chain size and polymer concentration profile, especially for the fast polymerization. End-to-end distance of chains of similar lengths increased with increasing pore radius and depended on the polymerization rate and brush average molecular weight. Distribution of free chain ends approximately followed polymer distribution in the brush with a maximum close to the pore surface.

Green production of cellular ceramics by emulsification of sunflower oil followed by gelcasting and starch consolidation

An environmentally friendly process combination for the production of alumina-based cellular ceramics is proposed. Biodegradable, renewable additives and low-energy conditions were applied. A fractional factorial design of 2 (4–1) + 3C was used to study the influence of gelatin, starch, and solids concentration, as well as water:oil ratio, on the rheological behavior of the suspension, and microstructural and mechanical features of cellular ceramics. A deflocculation curve was elaborated to define the best deflocculant concentration. The emulsions presented a rheopectic and pseudoplastic behavior. The sample with the highest open porosity was selected and analyzed by computer microtomography. SEM images showed open and closed spherical pores in the range of 7–22 μm for samples sintered at 1400 oC; 6–17 μm at 1550 °C, with respective open porosity values of 36–59% and 23–58%. Mean pore diameters estimated by μCT varied from 2 to 14 μm, with 78% at 1400 oC and 89% at 1550 oC. Compressive strength measured were 16–57 MPa (1400 oC), and 40–78 MPa (1550 oC). The combination of the three manufacturing methods was effective in the production of cellular ceramics with low energy, low amounts of gelling agents and low environmental costs.

Hybrid Three-Dimensional-Printed Ear Tissue Scaffold With Autologous Cartilage Mitigates Soft Tissue Complications.

To analyze the use of highly translatable three-dimensional (3D)-printed auricular scaffolds with and without novel cartilage tissue inserts in a rodent model. Preclinical rodent animal model. This prospective study assessed a single-stage 3D-printed auricular bioscaffold with or without porcine cartilage tissue inserts in an athymic rodent model. Digital Imaging and Communications in Medicine computed tomography images of a human auricle were segmented to create an external anatomic envelope filled with orthogonally interconnected spherical pores. Scaffolds with and without tissue inset sites were 3D printed by laser sintering bioresorbable polycaprolactone, then implanted subcutaneously in five rats for each group. Ten athymic rats were studied to a goal of 24 weeks postoperatively. Precise anatomic similarity and scaffold integrity were maintained in both scaffold conditions throughout experimentation with grossly visible tissue ingrowth and angiogenesis upon explantation. Cartilage-seeded scaffolds had relatively lower rates of nonsurgical site complications compared to unseeded scaffolds with relatively increased surgical site ulceration, though neither met statistical significance. Histology revealed robust soft tissue infiltration and vascularization in both seeded and unseeded scaffolds, and demonstrated impressive maintenance of viable cartilage in cartilage-seeded scaffolds. Radiology confirmed soft tissue infiltration in all scaffolds, and biomechanical modeling suggested amelioration of stress in scaffolds implanted with cartilage. A hybrid approach incorporating cartilage insets into 3D-printed bioscaffolds suggests enhanced clinical and histological outcomes. These data demonstrate the potential to integrate point-of-care tissue engineering techniques into 3D printing to generate alternatives to current reconstructive surgery techniques and avoid the demands of traditional tissue engineering. NA Laryngoscope, 131:1008-1015, 2021.

Effective properties of a porous inhomogeneously polarized by direction piezoceramic material with full metalized pore boundaries: Finite element analysis

This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces. To determine the effective properties, we used the effective moduli method and the finite element approaches, realized in the ANSYS package. As a simple model of the representative volume, we applied a unit cell of porous piezoceramic material in the form of a cube with one spherical pore. We modeled metallization by introducing an additional layer of material with very large permittivity coefficients along the pore boundary. Then we simulated the nonuniform polarization field around the pore. For taking this effect into account, we previously solved the electrostatic problem for a porous dielectric material with the same geometric structure. From this problem, we obtained the polarization field in the porous piezomaterial; after that, we modified the material properties of the finite elements from dielectric to piezoelectric with element coordinate systems whose corresponding axes rotated along the polarization vectors. As a result, we obtained the porous unit cell of an inhomogeneously polarized piezoceramic matrix. From the solutions of these homogenization problems, we observed that the examined porous piezoceramics composite with metalized pore boundaries has more extensive effective transverse and shear piezomoduli, and effective dielectric constants compared to the conventional porous piezoceramics. The analysis also showed that the effect of the polarization field inhomogeneity is insignificant on the ordinary porous piezoceramics; however, it is more significant on the porous piezoceramics with metalized pore surfaces.

An Algorithm to Optimize the Micro-Geometrical Dimensions of Scaffolds with Spherical Pores.

Despite the wide use of scaffolds with spherical pores in the clinical context, no studies are reported in the literature that optimize the micro-architecture dimensions of such scaffolds to maximize the amounts of neo-formed bone. In this study, a mechanobiology-based optimization algorithm was implemented to determine the optimal geometry of scaffolds with spherical pores subjected to both compression and shear loading. We found that these scaffolds are particularly suited to bear shear loads; the amounts of bone predicted to form for this load type are, in fact, larger than those predicted in other scaffold geometries. Knowing the anthropometric characteristics of the patient, one can hypothesize the possible value of load acting on the scaffold that will be implanted and, through the proposed algorithm, determine the optimal dimensions of the scaffold that favor the formation of the largest amounts of bone. The proposed algorithm can guide and support the surgeon in the choice of a “personalized” scaffold that better suits the anthropometric characteristics of the patient, thus allowing to achieve a successful follow-up in the shortest possible time.

Controlled Synthesis of Porous Carbon Nanostructures with Tunable Closed Mesopores via a Silica-Assisted Coassembly Strategy

Controllable fabrication of mesoporous carbon nanoparticles (MCNs) with tunable pore structures is of great interest, due to the remarkable effect of pore structure on electrochemical performance o...

Fabrication of highly porous merwinite scaffold using the space holder method

In this study, for the first time, the space holder method was used to fabricate a 3D macroporous nanostructured merwinite scaffold with highly interconnected spherical pores. The nanostructured merwinite powders were prepared by the sol-gel method and an optimal calcination cycle was ascertained. The average values of true and apparent porosities of the prepared scaffolds calculated in the range 85–81% and 80–74%, respectively, while the macropore sizes are determined in the range of 400–600 μm. The compressive strength of the prepared scaffold was obtained to be about 0.18–0.29 MPa. Immersion testing in simulated body fluid proved the appropriate bioactivity and biodegradability of the prepared scaffolds. Our study indicated the merwinite scaffold possessed suitable mechanical strength along with highly porous structure and apatite-formation ability which could be used for bone tissue engineering applications.

Lightweight epoxy-based abradable seal coating with high bonding strength

To gain high efficiency and low fuel consumption, aluminum-based abradable seal coatings had been widely used in the compressor casing of aero engines or gas turbines owing to the low elastic modulus. However, the adhesive transfer phenomenon frequently occurs when the radial rubbing generates between titanium alloy blade tips and aluminum-based coating. It tends to increase scratch force and results in blades vibration and even engine jam. To eliminate this problem, a new lightweight epoxy-based abradable seal coating with high bonding strength was developed by an effective and porosity controllable mixing process that distributes spherical pores uniformly in the continuous matrix. A lightweight coating of 63% porosity with a hardness of 33.1(HR15Y) can be reached when the content of hollow microspheres is 31 wt.%. The coating density is 0.5 g/cm3 and the bonding strength is as high as 18 MPa. The performance of the epoxy-based coating is comprehensively better than aluminum-based coatings in five essential indices. This study is expected to provide a new technical path for obtaining high-quality abradable seal coatings to guarantee the efficient and safe operation of compressors.

Solvation pressure in spherical mesopores: Macroscopic theory and molecular simulations

AbstractFluids adsorbing in nanoporous solids cause high solvation pressures that deform the solids and affect properties of the fluids themselves. We calculate solvation pressure of nitrogen adsorbed at 77.4 K in spherical silica mesopores using two methods: the macroscopic Derjaguin–Broekhoff–de Boer theory and molecular simulations. We show that both approaches give consistent results, and the observed pressures increase in smaller pores reaching the order of a hundred megapascals. The results are also typical for the solvation pressure in mesoporous materials, yet noticeably differ from the results for the cylindrical pore geometry. Furthermore, we show that the dependence of the solvation pressure at saturation on the reciprocal pore size is linear, and we use this relation for the calculation of the solid–liquid surface energy. The results can be employed for the prediction of the solvation pressure and the adsorption‐induced deformation in the material with the spherical pore geometry.

Characterizing the shape, size, and distribution heterogeneity of pore-fractures in high rank coal based on X-ray CT image analysis and mercury intrusion porosimetry

The shape, size, and surface characters of pore-fractures in coal are the basis for understanding the occurrence and migration of coalbed methane (CBM), which requires quantitative characterization. In this study, X-ray CT image analysis was used to quantitatively characterize the size distribution and volume contribution of pore-fractures in coal at three cohesive-scales (nanometer-scale, micrometer-scale, and macro-scale). A shape factor was introduced to divide the pore-fracture shapes into five types: spherical, tubular, slot, and slit pores and flat fractures, which mainly develop in diameters of 0.2–0.8 μm, 0.8–10 μm, 10–30 μm, 30–40 μm, and 50–240 μm, respectively. Compared to mercury intrusion porosimetry (MIP), it was found that the pore diameters measured by X-ray CT image analysis were relatively larger, the pore volume contribution increased then decreased with increasing pore diameter, and pores with diameters of 10–30 μm were the largest. When the pore diameter is 0.2–1 μm and 30–40 μm, the specific surface area by X-ray CT image analysis was 20.38% and 51.53% higher than that from MIP. When the pore diameter is 1–10 μm, the specific surface area measured by the two methods were similar. When the pore diameter is 10–30 μm, the specific surface area by MIP was 43.02% higher than that from X-ray CT image analysis. X-ray CT image analysis is more suitable for testing the morphologies than MIP. Additionally, these shape models of pore-fractures in this work can provide some understanding for the permeability calculations.

Review of Laser Powder Bed Fusion of Gamma-Prime-Strengthened Nickel-Based Superalloys

This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.

Key Factor Study for Amphiphilic Block Copolymer‐Templated Mesoporous SnO2 Thin Film Synthesis: Influence of Solvent and Catalyst

AbstractAs a crucial material in the field of energy storage, SnO2 thin films are widely applied in daily life and have been in the focus of scientific research. Compared to the planar counterpart, mesoporous SnO2 thin films with high specific surface area possess more attractive physical and chemical properties. In the present work, a novel amphiphilic block copolymer‐assisted sol–gel chemistry is utilized for the synthesis of porous tin oxide (SnO2). Two key factors for the sol–gel stock solution preparation, the solvent category and the catalyst content, are systematically varied to tune the thin film morphologies. A calcination process is performed to remove the polymer template at 500 °C in ambient conditions. The surface morphology and the buried inner structure are probed with scanning electron microscope and grazing‐incidence small‐angle X‐ray scattering. Crystallinity is characterized by X‐ray diffraction. The multi‐dimensional characterization results suggest that cassiterite SnO2 with spherical, cylindrical, and vesicular pore structures are obtained. The variation of the film morphology is governed by the preferential affinity of the utilized solvent mixture and the hydrogen bond interaction between the employed cycloether and H2O molecules in the solution.