Interlayer Porosity Research Articles

Interlayer bonding performance of 3D printed engineered cementitious composites (ECC): Rheological regulation and fiber hybridization

The weak interlayer adhesion caused by the layer-by-layer 3D printing (3DP) process and the incorporation of organic fiber in Engineered Cementitious Composites (ECC), detrimentally impacts the integrity of 3DP-ECC structures, particularly for large-scale structures requiring extended open time. To optimize the printing quality and extent the operation time, cellulose filaments (CF) were employed as nano-reinforcement, viscosity modifier and water retainer, and were hybridized with polyethylene fiber (PE) and steel fiber (ST). The highest bonding strength was raised up to 3.51 MPa. The time-dependent escalation of rheological parameters was mitigated, reducing interlayer porosity to 0.56 % and limiting the reduction in bonding strength to 12.01 % within 60 min open time. The compressive anisotropy was almost eliminated, verifying the potential of CF in modifying interlayer adhesion. A linear correlation between rheological behavior and interlayer bonding performance was established, and a 0.508 Pa s/min plastic viscosity growth rate was suggested to avoid cold joint and ensure printing quality.

Exploring the potential of metal tailored imine based covalent organic framework for asymmetric supercapacitor applications

Currently, a fascinating area of research involves the development of stable and efficient materials for energy storage systems. The current work describes the synthesis of imine linked covalent organic framework (COF) using 4,4′,4′',4′''-(ethene-1,1,2,2-tetrayl) tetraaniline and terephthalaldehyde (TAT-COF) as precursors through solvothermal method. In addition, cobalt has been integrated to the imine linkage of TAT-COF to generate CO@TAT-COF. The X-ray diffraction study reveals the formation of ordered and crystalline TAT-COF with eclipsed (AA) stacking configuration. Morphological characterization indicated the accumulation of metal species over stick like structured TAT-COF. Energy-dispersive X-ray (EDX) and Fourier Transform Infrared Spectroscopy results shows the successive intercalation of Co to the TAT-COF matrix. TAT-COF and Co@TAT-COF were examined towards electrochemical performance for supercapacitor applications. A two fold higher specific capacitance (Csp) was obtained in Co@TAT-COF (637 F/g) compared to TAT-COF (315 F/g) at 5 mV/s scan rate. The Co@TAT-COF showed an energy density (ED) of 58 Wh/kg at a power density of (PD) of 1500 W/kg. Enhanced electrochemical performance in Co@TAT-COF could be attributed to the structural confinement, conductivity, enhanced interlayer spacing and porosity. Co@TAT-COF has been used as positive electrode to fabricate an asymmetric device (ASD) in using Swagelok cell. The Csp of the fabricated ASD was found to be 95 F/g at 2 mV/s scan rate. ASD showed good stability with 73 % retention of Csp over 5000 charge/discharge cycles. The obtained results indicate the suitability of the engineered COFs towards energy storage devices.

Thermodynamic Coupling Forming Performance of Short Fiber-Reinforced PEEK by Additive Manufacturing.

In this work, the PEEK/short carbon fiber (CF) composites were prepared, a new thermodynamic coupling (preheating and impact compaction) process of the FDM method is proposed, and the warp deformation mechanism was obtained by finite element simulation analysis. Results show that a new method could improve the forming quality of an FDM sample. The porosity of FDM samples of the PEEK/CF composite gradually decreased from 10.15% to 6.83% with the increase in impact temperature and frequency. However, the interlayer bonding performance was reduced from 16.9 MPa to 8.50 MPa, which was attributed to the influence of the printing layer height change from the printhead to the forming layer. To explain the above phenomenon, a thermodynamic coupling model was established and a relevant mechanism was analyzed to better understand the interlayer mechanical and porosity properties of PEEK/CF composites. The study reported here provides a reference for improving the forming quality of fabricated PEEK/CF composites by FDM.

Influence of salinity gradients on the diffusion of water and ionic species in dual porosity clay samples

Most of the available data on diffusion in natural clayey rocks consider tracer diffusion in the absence of a salinity gradient despite the fact that such gradients are frequently found in natural and engineered subsurface environments. To assess the role of such gradients on the diffusion properties of clayey materials, through-diffusion experiments were carried out in the presence and absence of a salinity gradient using salt-diffusion and radioisotope tracer techniques. The experiments were carried out with vermiculite samples that contained equal proportions of interparticle and interlayer porosities so as to assess also the role played by the two types of porosities on the diffusion of water and ions. Data were interpreted using both a classical Fickian diffusion model and with a reactive transport code, CrunchClay that can handle multi-porosity diffusion processes in the presence of charged surfaces. By combining experimental and simulated data, we demonstrated that (i) the flux of water diffusing through vermiculite interlayer porosity was minor compared to that diffusing through the interparticle porosity, and (ii) a model considering at least three types of porous volumes (interlayer, interparticle diffuse layer, and bulk interparticle) was necessary to reproduce consistently the variations of neutral and charged species diffusion as a function of salinity gradient conditions.

Reversible Constrained Dissociation and Reassembly of MXene Films.

Enabling materials to undergo reversible dynamic transformations akin to the behaviors of living organisms represents a critical challenge in the field of material assembly. The pursuit of such capabilities using conventional materials has largely been met with limited success. Herein, the discovery of reversible constrained dissociation and reconfiguration in MXene films, offering an effective solution to overcome this obstacle is reported. Specifically, MXene films permit rapid intercalation of water molecules between their distinctive layers, resulting in a significant expansion and exhibiting confined dissociation within constrained spaces. Meanwhile, the process of capillary compression driven by water evaporation reinstates the dissociated MXene film to its original compact state. Further, the adhesive properties emerging from the confined disassociation of MXene films can spontaneously induce fusion between separate films. Utilizing this attribute, complex structures of MXene films can be effortlessly foamed and interlayer porosity precisely controlled, using only water as the inducer. Additionally, a parallel phenomenon has been identified in graphene oxide films. This work not only provides fresh insights into the microscopic mechanisms of 2D materials such as MXene but also paves a transformative path for their macroscopic assembly applications in the future.

Microstructure evolution and mechanical properties of wire-arc-additively manufactured Al–Cu–Mg–Ag alloy

In this article, Al–Cu–Mg–Ag specimens were successfully wire-arc-additive-manufactured based on by gas metal arc process to investigate the evolution of microstructure and mechanical properties. The results showed that the grain morphology and pore size in the printed specimens varied in height direction. Under the influence of repeated thermal cycling, which affected the solid-state diffusion of the deviated elements at the grain boundaries, the distribution of the nanoscale second phase appeared significantly different in the height direction. The precipitation phase changes caused the microhardness of the printed specimens to decrease gradually from a peak of 125 HV and stabilise at around 100 HV. The changes in the printed specimens’ horizontal mechanical properties were insignificant mainly due to interlayer porosity.

3D printed concrete with sewage sludge ash: Fresh and hardened properties

In this study, the possibility of application of sewage sludge ash (SSA) in 3D printed concrete (3DCP) technology was explored. The replacement of partial cement with SSA in the concrete mix design was investigated, followed by a comprehensive analysis of its impact on the workability, printability, and mechanical properties of the 3DCP. The findings indicated that the incorporation of SSA accelerated the loss of workability of 3DCP, such as fluidity and consistency. However, it significantly improved the green strength and buildability. Further investigation revealed that the addition of SSA hampered the hydration process of cement, resulting in a reduction in the mechanical properties of the hardened material. CT scanning indicated that the addition of SSA increased the interlayer porosity, leading to further degradation of the mechanical properties. The toxicity characteristic leaching procedure demonstrated that the maximum leaching concentration of 3DCP incorporating SSA was 0.14 mg/L. This result confirmed the effective immobilization of heavy metals, fulfilling the prerequisites for the application of 3DCP incorporating SSA.

A way for densification of lead-free BaTiO3-based/ZrO2 laminates for energy harvesting applications prepared by electrophoretic deposition

In this paper, the concept of multi-layer ceramics based on a combination of piezoelectric layers BaTiO3 (BT) or (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) alternated with mechanically durable ZrO2 (Z) layers is investigated. Both BT/Z and BCZT/Z laminates were successfully electrophoretically deposited (EPD) due to knowledge of the deposition kinetics of individual materials and their green densities allowing precise layer thickness control. The EPD was followed by conventional sintering (CS) or spark plasma sintering (SPS). The CS resulted in the development of cracks, pores, and significant chemical reactions at the layers interfaces in both types of laminates. Laminates sintered by SPS were crack free with suppressed or none chemical reactions at the interfaces. The mechanical properties development across layers was monitored using nanoindentation. This approach identified interlayer porosity evolution and estimated the significance of the reaction zone at the interface.

In-operando X-ray scattering characterization of smectite swelling experiments

Swelling capacity of smectite was studied over decades regarding its application as barrier in disposal of nuclear wastes in geological repositories as well as the induced volume change potential in soils according to moisture. In order to improve our knowledge in the swelling capacity of smectite, a miniaturized oedometer was developed to combine swelling pressure measurement with wide angle X-ray scattering (WAXS) characterization in real time during hydration of smectite. This coupled set up allowed studying hydration of smectite up to saturation under confined condions and linking crystalline swelling to pressure at various densities. The modeling of the WAXS patterns gave also quantitative information about the relative proportion of the different interlayer water types at saturation. In situ and operando data were acquired for homo-ionic Na+- and Ca2+-exchanged smectite at two different densities (1.5 and 1.8 g/cm3). The results showed that the swelling pressure rise was correlated to a sequence of water layer type with the transition from 0W to interstratification of 2W/3W layers, depending on the density. The cation valency controlled the rate of hydration with faster hydration in the case of divalent exchanged smectite. At saturation, with increasing density, the amount of 3W layers decreased to the gain of 1W and 0W layers. Results also confirmed that at saturation and a density of 1.8 g/cm3, the interlayer porosity represented the total one. Finally, this development provided opportunity to improve our knowledge in the swelling mechanism of compacted swelling clay materials upon hydration.

Experimental and modeling study of the diffusion path of Ce(III)-EDTA in compacted bentonite

The impact of the diffuse double-layer on the diffusion of radionuclide anions remains unclear, impeding the application of Archie's law for adsorptive anions. Through-diffusion experiments were carried out to measure the effective diffusion coefficient and distribution coefficient of Ce(III) in the presence of EDTA. A multi-porosity model, in combination with Archie's law, was used to estimate the effective diffusion coefficient. The predominant species, CeEDTA−, exhibited an effective diffusion coefficient of (0.88–1.92) × 10−11 m2/s and the distribution coefficient of (0.81–1.18) × 10−3 m3/kg at the compacted dry density of 1300–1800 kg/m3. The accessible porosity, the diffuse double-layer porosity, and the interlayer porosity were analyzed using the multi-porosity model, based on the characterization of bentonite via Scanning electron microscopy with energy dispersive spectrometry, X-ray diffractometer, and Nitrogen-Brunner-Emmett-Teller method. Due to the low external surface area of Zhisin bentonite (27.7–35.3 m2/g), the impact of the diffuse double-layer was insignificant on the total and accessible porosities. Additionally, the diffuse double-layer porosity had insignificant impact on the effective diffusion coefficient of CeEDTA− in compacted bentonite, as its value was one order magnitude lower than that of the interlayer porosity and the accessible porosity.

Using Fibre recovered from face mask waste to improve printability in 3D concrete printing

Surgical face mask usage has rapidly increased in the last two years due to the COVID-19 pandemic. This generates vast amounts of plastic waste, causing significant risks to the ecosystem. Thus, this study assesses the potential of using recycled fibre from face mask waste as fibre reinforcement in 3D concrete printing (3DCP) applications to improve printability while reducing landfill waste. The effect of recycled fibre from waste face masks on the rheological characteristics of printable mixes and the mechanical performance of printed elements was evaluated for different contents of shredded face masks (i.e., 1% and 2% by vol). The rheological properties like static and dynamic yield strengths, apparent viscosity, and thixotropic behaviour, along with compressive and flexural strength, were evaluated for 3D printed specimens and mechanical properties were compared to their mould-cast counterparts. Further, the variation in the interlayer bond strength and porosity due to different fibre dosages was also investigated. In addition, a comparative study on the fresh and hardened properties was performed for the printable mixes with polypropylene (PP) fibres and face masks. The addition of face masks significantly improved the rheological properties with good extrudability and buildability for all the dosages. Compared to face masks, mixes with PP fibres showed poor extrudability with higher fibre dosages. The compressive strength was increased by 41% for a 1% dosage of face masks when compared to the unreinforced concrete. Furthermore, the flexural strength when tested along the weaker interface, showed an increase of 74% and 82% for the addition of 1% and 2% face mask content. The interlayer bond strength of 1% face mask content showed 21% improvement and was observed to have the highest surface moisture content. The mechanical performance of face masks and PP fibres are observed to be comparable for 1% dosage. The mechanical properties of printed and mould-cast specimens were also observed to be similar.

Elucidating laser directed energy deposition based additive manufacturing of copper-stainless steel functionally graded material: Processing and material behavior

Copper (Cu)-stainless steel (SS 304L) multi-material is enduring research topic for various engineering applications such as tooling industry, aerospace, power-generation and cryogenic applications. Laser directed energy deposition (LDED) based additive manufacturing is a one of the promising technologies for fabricating Cu-SS multi-material component. However, LDED of Cu-SS is difficult due to the significant difference in thermo-physical properties and poor solubility of Cu and Fe. One of the methods to overcome this issue is adopting a functionally graded material (FGM) approach. In this pretext, the fabrication of Cu-SS FGM using the LDED process is taken up in the present study with three different Cu compositional grading approaches, such as direct (GD100Cu), 50 % (GD50Cu) and 20 % (GD20Cu). The LDED process windows for single tracks and bulk deposition of Cu-SS FGM are identified by varying the laser power, scan speed and composition of Cu and SS304L. Subsequently, the identified process window is used to deposit bulk structures of Cu-SS FGM. The LDED-built Cu-SS FGMs are characterized in terms of build quality, chemical composition, microstructural evolution and mechanical behavior. Microscopic analysis reveals, the defect-free deposition of GD100Cu and GD50Cu, at identified process parameters. For GD20Cu, the micro-crack formation in the graded region and inter-layer porosity in the Cu-rich region are two competing phenomenon, and it is observed that layer-wise increase in laser power and interlayer delay leads to minimum crack density and lower porosity. Further, increase in Cu content leads to significant change in microstructural morphology from columnar dendrites to fine cellular morphology. In Cu-SS FG structures, the chemical composition and mechanical properties are found to be changing gradually. Further, obtained ultimate tensile strength (UTS) of GD100Cu and GD50Cu is found higher than GD20Cu and the mode of failure is found to be ductile. The improved UTS in GD100Cu and GD50Cu in comparison with pure Cu arises due to formation of nano precipitate of Cu in the inter-dendritic zone of Fe rich phase. This establishes the suitability of LDED for building FG Cu-SS components at GD50Cu over GD20Cu.

The Relationship Between Fiber Bundle Size and Mechanical Performance of Additively Manufactured Continuous Carbon Fiber Reinforced Thermoplastic Composites.

Additively manufactured continuous fiber-reinforced thermoplastic (CFRTP) composites are still in the early stages of reaching competitive mechanical properties compared with conventional composites. The main reason for this is that their mechanical properties are limited due to weak interlayer strength, porosity, and low fiber fraction. Therefore, the effects of many parameters, such as layer thickness, temperature, printing speed, and fiber fraction, have been extensively studied to improve mechanical properties. With a different perspective on these parameters, this study aimed to investigate the effect of fiber bundle size on the mechanical properties of CFRTP composites. For this purpose, 3K and 6K fiber bundle filaments with the same fiber volume fractions (∼41%) were produced utilizing a polymer impregnation setup. CFRTP samples were printed using fused deposition modeling with polylactic acid as the matrix. The mechanical properties were investigated via three-point bending, interlaminar shear strength (ILSS), and tensile tests. The results showed that fiber bundle size does not particularly influence tensile strength but dominates flexural and ILSS performance. Although increased flexural strength and modulus were observed, the bundle size effect was much more dominant in ILSS tests, and 6K bundle size samples with the same fiber fraction showed much higher strength.

Fabrication Temperature-Related Porosity Effects on the Mechanical Properties of Additively Manufactured CFRP Composites

The use of additive manufacturing in fabricating composite components has been gaining traction in the past decade. However, some issues with mechanical performance still need to be resolved. The issue of material porosity remains a pertinent one which needs more understanding to be able to come up with more viable solutions. Different researchers have examined the subject; however, more research to quantitatively determine fabrication temperatures effects at the micro-scale are still needed. This study employed micro-CT scan analysis to quantitatively compare fabrication temperatures effect at 230 °C, 250 °C, 270 °C, and 290 °C on the mechanical properties of AM fabricated carbon-fiber-reinforces plastic (CFRP) composites, testing carbon fiber-reinforced polyamide (CF-PA) and carbon fiber-reinforced acrylonitrile butadiene styrene (CF-ABS) samples. This micro-CT examination followed an SEM evaluation, which was used to determine temperature effects on interlayer and intralayer porosity generation. The porosity volume was related to the mechanical properties, in which it was determined how temperatures influence porosity volumes. It was also determined that fabrication temperature generally affects semicrystalline composites more than amorphous composites. The overall porosity volumes from the interlayer and intralayer voids were determined, with the interlayer voids being more influential in influencing the mechanical properties.

Porosity investigation of compacted bentonite using through-diffusion method and multi-porosity model

The diffusion behavior of ReO4− and HSeO3− in low-grade bentonites was firstly investigated under different compacted dry densities. The effective diffusion coefficient, the accessible porosity, and the rock capacity factor were measured by a through-diffusion method. The effective diffusion coefficient was approximately three times in Zhisin bentonite with 36.8 wt% of montmorillonite than that in GMZ bentonite with 74.5 wt% of montmorillonite. The porosity distribution of the compacted bentonite was analyzed by a multi-porosity model. The effects of the compacted dry density, the ionic strength, and the stacking number on porosities were discussed. The compacted dry density had obvious influence on the accessible porosity, the diffuse double layer porosity, and the interlayer porosity. The effects of ionic strength and stacking number were mainly on the diffuse double layer porosity, leading to the alteration of the accessible porosity and the effective diffusion coefficient. Moreover, the multi-porosity model could successfully predict the trend of effective diffusion coefficient in compacted bentonite combined with Archie law, which provides a useful tool to understand the relationship between the microstructure of montmorillonite and the diffusion of radionuclide anions.

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

Insight into the microstructural and durability characteristics of 3D printed concrete: Cast versus printed specimens

This study presents the comparison of microstructural and durability characteristics of 3D printed concrete (3DPC) depending on its production method (printing or casting). Printed samples with different numbers of layers, as well as a cast specimen with an identical mix composition, were produced and compared, with their microstructural pore and solid characteristics quantitatively and qualitatively investigated. For this purpose, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) were utilized to evaluate the microstructures of the 3DPC. In particular, quantitative approaches using micro-CT data were newly proposed for a better understanding of the microstructural characteristics of 3DPC. Moreover, their durability-related characteristics and transport properties, including freeze-thaw and thermal resistance, were examined and compared. Despite noticeable differences between the microstructures of the printed and cast specimens, including their anisotropic and inter-layer porosity and heterogeneity, confirmed by MIP, SEM and micro-CT, no significant differences in the transport (capillary water porosity and water sorptivity) or durability-related properties (frost and thermal attack) were found. This was due to the dense and homogenous microstructure of 3DPC, which is attributable to the high binder content and low w/b of the mixture. Moreover, the newly proposed evaluation provided reasonable quantitative and qualitative characteristics, which can be used to demonstrate and predict the material properties of 3DPC.

Effect of sulphoaluminate cement on fresh and hardened properties of 3D printing foamed concrete

Generally, we expect that cement-based materials for 3D printing can quickly obtain sufficient strength after extrusion to resist the pressure generated by the stacking layers to achieve good buildability. In this study, sulphoaluminate cement (SAC) was used to improve the printability of fresh foamed concrete (FC). The effects of different SAC contents on the foam stability, open time, and buildability of fresh FC, the interlayer interface, and porosity and mechanical anisotropy of hardened 3D printed FC (3DPFC) were investigated. The addition of SAC reduces the settlement of fresh FC and prevents defoaming by promoting the hydration process to accelerate the formation of pore structure . In addition, SAC reduces the bubble diameter of the fresh FC, which is attributed to the enhancement of yield stress of the mortar before doping foam. Meanwhile, the buildability of 3DPFC is improved, while the open time is reduced with the addition of SAC. The printability of the 3DPFC can be predicted based on the remaining height of the FC from cylinder test and the flow diameter from jumping table test. When the remaining height is 74–80 mm, and the flow diameter is between 155 and 176 mm, the extrudability and buildability of the 3DPFC can be guaranteed simultaneously. With an increase in SAC content, the width of the interface area and the interface porosity of the 3DPFC increase, leading to the intensification of mechanical anisotropy. We suggest that the SAC content for 3DPFC should not exceed 10%.

Effects of extrusion parameters on properties of 3D printing concrete with coarse aggregates

Different extrusion systems have been widely used in previous studies, researches on the influence of nozzle directions and scrapers on properties of 3D printing concrete (3DPC) were however very limited. Therefore, the buildability, mechanical properties, and microstructure of concrete printed by different nozzle directions and scrapers were studied in this investigation. It has been found that the vertical extrusion force would reduce buildability, whereas increase the mechanical properties of 3DPC. Microstructure indicates that the interlayer porosity of concrete printed by vertical nozzle is 79.8% of that printed by horizontal nozzle. Besides, compared with the vertical nozzle without scraper (VN), the vertical nozzle with 40 mm-height scrapers (VN-40S) could reduce the vertical deformation of 3DPC by 20%−25% and increase the flexural strength parallel to the printing direction of 3DPC by 44%–49%. The interlayer porosity of concrete printed by VN-40S is 70.1% of that printed by VN. Longer scrapers could influence more printed layer fresh concrete, so the porosity is further reduced. Finally, a discrete element method (DEM) and automatic scraper system are discussed for the future work of 3DPC.

Study on Geometry, Dimensional Accuracy and Structure of Parts Produced by Multi Jet Fusion.

Multi Jet Fusion (MJF) is one of the newest additive manufacturing technologies for polymer powders, introduced in recent years. This fully industrial technology is gaining big interest as it allows fast, layer-by-layer, printing process, short production cycle, and very high printing resolution. In this paper, twelve thin-walled, spherical PA12 prints were studied in terms of geometry, dimensional accuracy, and fracture surface characteristics. The various characteristic features for MJF prints were observed here for parts produced according to four various print orientations and having different thicknesses, i.e., 1, 2 or 3 mm. The study showed that MJF technology can print such difficult shapes. However, the set of parameters allowing producing parts with highest geometrical and dimensional accuracy causes at the same time some microstructural issues, like great interlayer porosity or high number of non-processed powder particles embedded in the print structure.