Internal Void Formation Research Articles

Optimization of Steaming Conditions for Bellflower Root (Platycodon grandiflorus) Using K-Means Clustering-Based Morphological Grading System

Bellflower roots were categorized into three clusters (class 0, class 1, and class 2) using K-means clustering based on their morphological factors: length (282.8 ± 29.53, 138.75 ± 26.8, and 209.89 ± 20.49 mm), thickness (16.25 ± 2.82, 16.77 ± 3.35, and 16.52 ± 3.05 mm), and body shape coefficient (5.80 ± 1.15, 12.73 ± 4.82, and 7.95 ± 1.71). Internal void formation, a key quality factor for bellflower root, was analyzed under pre-steaming conditions, identifying temperatures between 20 and 25 °C as optimal for storage. Within the clustered class, steaming for a prolonged duration increased the formation of internal voids and caused a decrease in normal stress values, total dissolved solids (TDS), and pectin content. Class 0, with larger and thicker roots, exhibited higher internal voids (57% void rate) due to uneven heat distribution and incomplete starch gelatinization. Class 2 roots demonstrated better structural integrity, with a void rate of 26% and a stress value of 48 kN/m2. These findings highlight the importance of morphological classification and optimal storage temperatures to improve the quality of steamed bellflower roots.

Enhanced Mechanical Properties with Ag Addition in Electroplated Ni-Sn Solder Joints: Sub-10 Micron Bond Thickness

Keywords: Micro-bump; Microstructure; Intermetallic compounds; Mechanical properties; thermocompression bondingThe advancement of electronic devices has garnered more extensive attention towards three-dimensional integrated circuit (3D-IC) technology due to microbump size reduction and increased power density. Microbumps play an important role in driving the development of this technology, especially in 3D chip-stacking involving multiple reflow processes. The reduction in microbump height spotlights the presence of intermetallic compounds (IMCs). In comparison to traditional ball grid array (BGA) solder joints, microbumps with smaller solder volumes exhibit a predominant fraction of IMCs at solder joints, especially with microbump dimensions potentially shrinking to less than 10 micrometers.The interface reaction within confined spaces has become a critical concern. Mechanical properties will be dominated by IMC properties rather than solder characteristics. In conventional Cu/Sn/Cu solder joints, grain coarsening and prolonged reflowing times, which result in IMC collisions from opposing substrates, forming columnar grains with a uniform orientation, make the solder joint less reliable. Furthermore, the Cu3Sn layer in Cu/Sn/Cu microbumps presents another challenges, indicating the formation of Kirkendall voids, increasing the risk of brittle interface fractures.This study investigates the mechanical reliability and microstructure of two sub-10um sandwiched structures: Cu/Ni/Sn/Ni/Cu and Cu/Ni/Sn-3.5Ag/Ni/Cu. In the 3D-IC manufacturing process, solder joints will experience multiple reflow processing. Different reflow heat treatment process to achieve different fractions of Ni3Sn4 IMCs were performed on both sandwiched structure. Despite the formation of internal voids due to volume shrinkage in Ni/Sn solder joints, the addition of silver in the solder, forming Ag3Sn, effectively fills these voids. The long-time reflowed sample showed outstanding mechanical properties via the addition of silver in solder. In this study, the influence of silver addition on the microstructure and mechanical properties of the overall joints under identical reflow conditions, the fracture path observation after shear test were investigated. The growth mechanism of Ag3Sn and its distribution in the solder would be further explored and addressed. Figure 1

Micro-computed tomographic assessment of the influence of light-curing modes on internal void formation in bulk-fill composites

Micro-computed tomographic assessment of the influence of light-curing modes on internal void formation in bulk-fill composites

Impact of processing defects on microstructure, surface quality, and tribological performance in 3D printed polymers

Additive manufacturing (AM), also known as three-dimensional (3D) printing, of polymer-based materials is growing as a time-efficient, economical, and environmentally sustainable technique for prototype development in load-bearing applications. This work investigates the defects arising from the processing in material extrusion-based AM of polymers and their impact on the part performance. The influence of raster angle orientation and printing speed on tribological characteristics, microstructure, and surface finish of acrylonitrile butadiene styrene (ABS) fabricated in a heated build chamber was studied. Comprehensive analysis with fractography and tomography revealed the formation, distribution, and locations of internal voids, while surface defects were studied with the topography analysis of as-printed surfaces. Surface roughness and tribological results show that printing speed can be optimally increased with a minimal impact on interlayer bonding and part performance. Increased printing speed allowed up to 58% effective reduction in printing time obtaining comparable mechanical properties at varying process parameters. 3D printed ABS exhibited dry sliding friction coefficients in the range of 0.18–0.23, whilst the maximum specific wear rate was 6.2 × 10−5 mm3/Nm. Higher surface roughness and increased printing speed exhibited delayed running-in during dry sliding, while insignificant influence was observed for steady-state friction and wear behaviors. The findings indicate that improved surface finish and reduced internal defects can be achieved with a controlled build environment allowing for higher printing speed. The observations in this study are evidence that 3D printing can be adapted for the sustainable manufacturing of polymeric components for tribological applications.

Highly permeable nanofilms with asymmetric multilayered structure engineered via amine-decorated interlayered interfacial polymerization

Tailormade polyamide (PA) membrane structures for ultrafast water transportation that possess excellent selectivity are promising for efficient water reclamation. In this study, an ultrathin (8 nm) and asymmetric PA nanofilm with a multilayer structure, where the back surface is a porous layer containing a spherically porous structure and the upper surface is a dense selective layer having nodular wrinkles, is engineered via amine-decorated interlayer-mediated interfacial polymerization (IP). The self-assembled network of strongly charged and highly hydrophilic ionomers exhibits strong attraction toward aqueous amine monomers, and temporally disrupts their diffusion by imposing a heterogeneous energy barrier toward the organic phase to be polymerized with acyl chloride monomers. This triggers a diffusion-driven instability that enables the formation of internal voids at the back surface of the PA nanofilm. The asymmetric PA membrane exhibits an improved water permeance of up to 12.5 L m−2 h−1 bar−1; this is 3-fold larger than that of the traditional PA membrane (4.4 L m−2 h−1 bar−1). Further, it has a high divalent salt rejection ratio of 98.9%, thus overcoming the trade-off among state-of-the-art nanofiltration membranes. The formation mechanism of such asymmetric PA nanofilms was clarified through multiscale theoretical simulations. These findings represent advances toward developing ultrapermeable membranes for highly efficient ion/molecular separation.

Study on the formation and prevention mechanism of internal voids in cross wedge rolling

Study on the formation and prevention mechanism of internal voids in cross wedge rolling

Effect of dispensing rate on internal void formation in restorations built with sonically activated resin composite

AbstractInternal void formation in sonically activated resin composite (SonicFill 2, Kavo Kerr, Orange, CA, USA) applied at three different extrusion force magnitudes was evaluated. Forty SonicFill 2 composite compules were divided into four groups according to dispensing method and magnitude of extrusion force as follows: No sonic energy/manual dispensing (FM) (control), sonic energy with low extrusion force (F1), sonic energy with medium extrusion force (F3), and sonic energy with high extrusion force (F5) (n = 10). For F1, F3, and F5, sonic energy was delivered using a SonicFill handpiece. For the control, no sonic energy was applied. Composites were placed into the molds and polymerized. Micro‐computed tomography scanning for intrarestoration void assessment was performed and intrarestoration void rates (%) were calculated. Data were statistically analyzed (α = 0.05). Sonic energy yielded lower intrarestoration void rates than that of the control (10.58% ± 1.74%) (p < 0.05). Intrarestoration void rates between F1 (8.11% ± 0.99%) and F3 (7.00% ± 0.95%) were similar (p > 0.05), whereas F5 (5.14 ± 0.91%) led to significantly lower void rates compared to F1 and F3 (p < 0.05). The highest extrusion force (F5) setting of the SonicFill handpiece caused the lowest internal void rates in SonicFill 2 resin composite restorations compared to those of the medium (F3) and lowest (F1) settings.

Updating of dry shielding of nuclear power plant reactor vessel

Introduction. Dry shielding is a cylindrical structure made of serpentinite concrete in a metal casing with an inner diameter of 5.6 m, an outer diameter of 6.7 m, and a height of 5.3 m, which surrounds the VVER reactor vessel in the vicinity of the core. The purpose of serpentinite concrete, containing an increased amount of chemically bound water, is to soften the spectrum of the neutron flux outside the reactor, increasing the fraction of thermal neutrons in the spectrum, which is necessary for the operation of ionization chambers (IR) of the reactor control and protection system. Dry shielding also performs the functions of radiation and thermal protection, reducing the flux of radiation on ordinary concrete of biological protection. Before the installation of the dry shielding in the reactor shaft, heat treatment (drying) of concrete is carried out at temperatures up to 250 °С to remove unbound water in order to avoid radiolysis. Quality control of concreting and then heat treatment is carried out using a radioisotope device — a neutron moisture meter. These works are very lengthy and costly. Materials and methods. The design of the dry shielding casing was considered in order to perform additional perforation in order to avoid the formation of air pockets during concreting. The possibility of using modern plasticizing additives was considered in order to minimize the consumption of mixing water and, as a result, free water in the body of serpentinite concrete. Results. The possibility of exclusion of the stages of quality control of concreting and heat treatment in their traditional form is shown. Additional perforation of the metal casing, its internal diaphragms in problem areas, the use of a mixture of 20 cm slump or more allows you to completely eliminate the formation of internal voids. According to preliminary estimates, given the intensity of radiation in the NW for a modern reactor with a capacity of 1200 MW, the intensity of the release of hydrogen outside the shell due to radiolysis does not pose any danger. The concentration of hydrogen in the air surrounding the dry shielding is many orders less of magnitude than the dangerous 4 %. Conclusions. The cost of work on the construction of the SZ power unit of a nuclear power plant with a capacity of 1000–1200 MW can be reduced by 70–100 million rubles, the duration of work by 5 months.

Kirkendall effect induced bifunctional hybrid electrocatalyst (Co9S8@MoS2/N-doped hollow carbon) for high performance overall water splitting

Rational design of electrocatalysts with the tuneable structural and electrocatalytic properties are essential to accomplish bifunctional activity of hydrogen and oxygen evolution reaction (HER/OER), and thus efficient water splitting systems. Here, we present a bifunctional hybrid electrocatalyst consisting of Co9S8 (OER-active) and MoS2 (HER-active) with the structural merits of hierarchical morphology, huge electrochemically active sites, and greater charge transfer ability. The structural features of the hybrid electrocatalyst (Co9S8@MoS2/N-doped hollow carbon) that is derived from metal organic framework (MOF) precursor are elaborately controlled by the temperature dependent-Kirkendall diffusion effect. Specifically, the imbalanced diffusion rates between two ionic species (Co2+ and S2−), confined in the MOF-precursor geometry, induces the formation of internal voids and outward growth of Co9S8 while retaining MoS2 layers on the surface. As a result, the hybrid electrocatalyst exhibits greatly enhanced HER (126 mV@−10 mA cm−2) and OER (233 mV@10 mA cm−2) performance. Furthermore, the bifunctional electrode couple demonstrates efficient overall water splitting performance (1.56 V@10 mA cm−2) compared to the benchmark electrode couple of IrO2/C//Pt/C (1.63 V@10 mA cm−2) in 1 M KOH solution. The results highlight that inducing “Kirkendall effect” through temperature-tuning approach for structure-properties modulation can be extensively applied to design various bifunctional hybrid electrocatalysts.

A facile approach for construction of hierarchical zeolites via kinetics

Abstract It has long been a dream to construct hierarchical zeolites by a really simple and cost-effective method which is feasible in industry. Here we provide an alternative approach in which the crystallization kinetics is regulated by solely changing the added amount of NaOH in the initial gel of a traditional zeolite and then the adjustment of the morphology and structure of the zeolite products is realized. This approach overcomes most of the limitations associated with the popular methods, such as complex operations and costly secondary templates. As an example, hierarchical ZSM-5 zeolite is prepared with using the most common raw materials and synthesis technology which used in the large-scale production of traditional zeolites. The crystallization process of the hierarchical ZSM-5 zeolite is investigated in detail and compared with the microporous zeolite. The results indicate that the increase of NaOH concentration in the synthesis system can enhance the rate of nucleation but the hierarchical pore structure can be formed only under the moderate concentration. The crystallization of the hierarchical ZSM-5 zeolite takes place by a chain of processes: (i) formation of wormlike precursors, (ii) aggregation of the precursors, (iii) condensation of the precursors and formation of internal voids, (iv) formation of external shell layers. The performance studies show that the obtained hierarchical ZSM-5 zeolite possesses significantly enhanced diffusion property and superior ability for catalytic cracking bulky molecules.

Micro-computed tomographic evaluation of the effects of pre-heating and sonic delivery on the internal void formation of bulk-fill composites.

The aim of this study was to compare the effects of conventional, sonic or pre-heating insertion techniques on internal void formation of bulk-fill composites with micro-computed tomography. Standardized cylindrical cavities were prepared in 160 human third molars. Four groups received different paste-like bulk-fill composites: SonicFill 2 (SF2); VisCalor Bulk (VCB); Filtek One Bulk-fill restorative (FBF); Tetric EvoCeram Bulk Fill (TEB); and a conventional posterior composite, Clearfil Majesty Posterior (CMP). A hybrid CAD/CAM block was selected as a control (n=10). Composite restorations were built according to each resin composite type and insertion technique (n=10). Micro-CT was used to assess internal void rates. Data was analyzed with two-way ANOVA and Tukey's multiple comparisons test (α=0.05). CAD/CAM blocks were free of voids. For each composite, the highest void rates were observed for the sonic delivery method (p<0.05) except for SF2. SF2 was not affected by insertion techniques (p>0.05). Other composites showed the lowest void rates with pre-heating technique.

Influence of die parameters on internal voids during multi-wedge-multi-pass cross-wedge rolling

The formation of internal voids in workpieces during cross-wedge rolling affects die design and limits their widespread applications. This article investigated the formation of internal voids during the multi-wedge-multi-pass rolling production of connecting rods. A three-dimensional numerical simulation model of cross-wedge rolling (CWR) was established using the rigid-plastic finite element method, and a density change model of the porous material was developed to characterize the degree of internal void formation in the connecting rod during CWR. The optimal die parameters (forming angle, spreading angle, and distribution coefficient of area reduction) were determined by determining their relationship to the density. The stress and strain of characteristic points near the loose longitudinal sections were used to study the void formation mechanisms. The accuracy of the numerical simulations was verified by rolling experiments, which showed no void formation in the internal sections of the connecting rod after production, confirming the feasibility of using this scheme to prevent void formation.

Assessment of the Mechanical Integrity of a 2 mm AA6060-T6 Butt Weld Produced Using the Hybrid Metal Extrusion &amp; Bonding (HYB) Process – Part I: Bend Test Results

Abstract The present investigation is concerned with butt welding of 2 mm thin AA6060-T6 profiles at room temperature (RT), using the HYB process and AA6082-T4 as filler material. In the as-welded condition, the 1000 mm long butt weld is seen to be straight and free from global distortions. At the same time both weld faces appear slick and display a nice surface finish. However, cold flow results in the formation of internal voids in the beginning of the weld, but these defects gradually disappear as the temperature distribution approaches pseudo-steady state further ahead. Still, root cracks evolved during instrumented three-point bend testing along the entire length of the weld because of “kissing” bond formation. Based on ABAQUS simulations of the bend test it is concluded that they form when the plastic tensile strain component on the root side of the weld exceeds about 0.38. Hence, the “kissing” bond formation is not devastating for the resulting mechanical integrity of the joint.

An investigation on the dissimilar friction stir welding of T-joints between AA5754 aluminum alloy and poly(methyl methacrylate)

Process optimization to prepare T-joints of poly methyl methacrylate (PMMA) and AA5754 alloy by friction stir welding (FSW) was performed. Effects of processing parameters including tool rotational velocity, traverse speed, tilt angle and plunge depth (TP) were studied. The material flow and formation of interaction layer upon FSW were evaluated and the tensile strength and hardness of the joints were examined. It is shown that by controlling the heat input into stir zone through increasing the rotational velocity or decreasing travelling speed, less defects are formed while the thickness of the interaction layer increases. The optimum condition is attained at 1600 rpm/30 mm min−1 with a tool tilt angle of 2° and plunge depth of 0.2 mm. Under this condition, the joint strength would reach ~71% (50 MPa) of the base polymer. It has been found that the thickness of the interaction layer and formation of internal voids have a remarkable influence on the strength and hardness of the T-joints. The presented results could be useful for development of dissimilar FSW of metal/polymer joints.

Micro‐computed tomography evaluation of internal void formation of bulk‐fill resin composites in Class II restorations

The aim of this study was to quantify the internal void volume formation in bulk‐fill resin composites with using 3D micro‐computed tomography (μCT). Class II box cavities in 4‐mm depth were prepared and treated with Clearfil S3 Bond Plus (Kuraray Medical). Five resin composites were evaluated: one conventional paste‐like (Filtek Ultimate Universal Restorative‐as the control), one conventional flowable (Filtek Ultimate Flowable Restorative), two flowable bulk‐fill (Voco Extrabase, SDR), one paste‐like bulk‐fill (Filtek One BulkFill Restorative). Resin composites were light cured using a light‐emitting diode light‐curing unit (SDI Radii Plus, SDI Limited, Australia). Samples were evaluated by μCT, and data were imported into software The NRecon (ver. 1.6.10.4, SkyScan) and CTAn (ver. 1.16.1.0, SkyScan) for 3D reconstruction, from which the percentage of void volume was calculated. Data were analyzed using the Kruskal‐Wallis test and the Mann–Whitney U‐test at a significance level of 5%. All restorative tested materials showed different levels of voids. Filtek One BulkFill Restorative showed the least void formation, which was statistically less than that of the conventional flowable composite group (p &lt; 0.05). All other restorative materials showed similar void formation. POLYM. COMPOS., 40:2984–2992, 2019. © 2018 Society of Plastics Engineers

Shrinkage and deformation during convective drying of calcium alginate

The effect of air temperature (40–70 °C) and gelation time (10–60 min) on drying kinetics and structure of calcium alginate (3 g/100 mL) particles dried in a convective packed bed drier were investigated. All drying conditions showed constant (initially) and decreasing drying rate periods during most of drying time. The drying time was reduced by a factor of 1.8 when increasing air temperature from 40 to 70 °C. Particle diameter decreased by 54–60% and was not affected by air temperature. However, the increase of drying rate due to a temperature beyond 40 °C resulted in formation of internal voids and higher shape deformation, i. e, it increased elongation and decreased roundness of the alginate particles. The formation of internal voids started in the transition between the constant and decreasing drying rate period. Besides, packed bed drying resulted in heterogeneous particles size distribution during intermediate drying times and more homogeneous size distribution in the end of the drying, when particles shrinkage is reduced. Finally, particles crosslinked during shorter gelation times presented less homogeneous structure, with irregular surface and collapsed center after drying, in comparison to longer gelation times.

Effects of GnF Concentration on the Mechanoelectrical Properties and Surface Morphology of GnF/PDMS Composites

The graphite nanoflake (GnF)-reinforced polydimethylsiloxane (PDMS) composites (GnF/PDMS composites) are developed as new polymer matrix composites (PMCs) with controllable mechanoelectrical properties. Here, we investigate the effect of GnF concentration on the mechanoelectrical properties (i.e., elastic modulus, fracture strain, and conductivity) of GnF/PDMS composites; the change in the surface morphology of GnF/PDMS composites caused by a variation in GnF concentration is also explored. The mechanoelectrical properties are measured by performing tensile tests on the GnF/PDMS composite specimens with different GnF concentrations of 5.0, 10.0, 12.5, 15.0, 20.0, and 25.0 wt.%. The surface morphology is analyzed in terms of internal void formation and surface roughness. The elastic modulus is measured to be in the range of 1.62 to 13.8 MPa which is proportional to GnF concentration, while the fracture strain and electrical conductivity are respectively characterized to be in ranges of 0.09 to 2.09 and 0.3 to 221.0 S/m which are in inverse proportion to GnF concentration. An increase in GnF concentration leads to increases in internal voids’ amount and surface roughness. The GnF/PDMS composites can be used as sensing materials for detecting both small and large deformations in a variety of engineering applications.

Ex-situ tracking solid oxide cell electrode microstructural evolution in a redox cycle by high resolution ptychographic nanotomography

For solid oxide fuel and electrolysis cells, precise tracking of 3D microstructural change in the electrodes during operation is considered critical to understand the complex relationship between electrode microstructure and performance. Here, for the first time, we report a significant step towards this aim by visualizing a complete redox cycle in a solid oxide cell (SOC) electrode. The experiment demonstrates synchrotron-based ptychography as a method of imaging SOC electrodes, providing an unprecedented combination of 3D image quality and spatial resolution among non-destructive imaging techniques. Spatially registered 3D reconstructions of the same location in the electrode clearly show the evolution of the microstructure from the pristine state to the oxidized state and to the reduced state. A complete mechanical destruction of the zirconia backbone is observed via grain boundary fracture, the nickel and pore networks undergo major reorganization and the formation of internal voids is observed in the nickel-oxide particles after the oxidation. These observations are discussed in terms of reaction kinetics, electrode mechanical stress and the consequences of redox cycling on electrode performance.

Real-time plasmon spectroscopy study of the solid-state oxidation and Kirkendall void formation in copper nanoparticles.

Oxidation and corrosion reactions have a major effect on the application of non-noble metals. Kinetic information and simple theoretical models are often insufficient for describing such processes in metals at the nanoscale, particularly in cases involving formation of internal voids (nano Kirkendall effect, NKE) during oxidation. Here we study the kinetics of solid-state oxidation of chemically-grown copper nanoparticles (NPs) by in situ localized surface plasmon resonance (LSPR) spectroscopy during isothermal annealing in the range 110-170 °C. We show that LSPR spectroscopy is highly effective in kinetic studies of such systems, enabling convenient in situ real-time measurements during oxidation. Change of the LSPR spectra throughout the oxidation follows a common pattern, observed for different temperatures, NP sizes and substrates. The well-defined initial Cu NP surface plasmon (SP) band red-shifts continuously with oxidation, while the extinction intensity initially increases to reach a maximum value at a characteristic oxidation time τ, after which the SP intensity continuously drops. The characteristic time τ is used as a scaling parameter for the kinetic analysis. Evolution of the SP wavelength and extinction intensity during oxidation at different temperatures follows the same kinetics when the oxidation time is normalized to τ, thus pointing to a general oxidation mechanism. The characteristic time τ is used to estimate the activation energy of the process, determined to be 144 ± 6 kJ mol-1, similar to previously reported values for high-temperature Cu thermal oxidation. The central role of the NKE in the solid-state oxidation process is revealed by electron microscopy, while formation of Cu2O as the major oxidation product is established by X-ray diffraction, XPS, and electrochemical measurements. The results indicate a transition of the oxidation mechanism from a Valensi-Carter (VC) to NKE mechanism with the degree of oxidation. To interpret the optical evolution during oxidation, Mie scattering solutions for metal core-oxide shell spherical particles are computed, considering formation of Kirkendall voids. The model calculations are in agreement with the experimental results, showing that the large red-shift of the LSPR band during oxidation is the result of Kirkendall voiding, thus establishing the major role of the NKE in determining the optical behavior of such systems.

Numerical and experimental studies of injection compression molding process for thick plastic gas valve stem

A crucial problem in injection molding of the thick plastic stem that is a key part of high-pressure gas valve is the formation of internal voids, because the structural failure of plastic stem owing to the internal voids not only deteriorates the operating function of gas valve but also may lead to the tremendous loss of financial and human resources. In this context, the goal of this study is to examine whether the formation of internal voids can be successfully suppressed when injection molding is replaced with injection compression molding. To examine this possibility, the major mold flow characteristics between injection molding and injection compression molding are firstly compared through 3-D thermal flow analyses. Next, for the sake of verification of numerical comparison, the plastic stem specimens are manufactured by both molding processes and the internal void formation is inspected using X-ray photos and cutting planes of specimens. Through the comparative numerical and experimental studies, it is confirmed that the crucial formation of internal voids in the conventional injection molding process can be successfully and completely removed by employing the injection compression molding.