Polycrystalline Research Articles

Correlating Frictional Forces Generated by Different Bracket Types during Sliding and Surface Topography Using Scanning Electron Microscopy and Optical Profilometer.

The study aims to correlate the frictional forces (FF) of four different types of commercially available ceramic brackets to their surface topography. Two monocrystalline (MC) brackets (CLEAR™, Adanta, Germany; Inspire ICE™, Ormco, USA), one polycrystalline (PC) bracket (Symetri Clear™, Ormco, USA), one clear hybrid esthetic bracket (DISCREET™, Adanta, Germany), and a stainless-steel (SS) bracket (Victory™, 3M Unitek, USA) served as control. Both static friction (SF) and kinetic friction (KF) were recorded during sliding using an Instron universal machine in dry settings. The bracket slot surface topography was evaluated. A scanning electron microscope (SEM) and a profilometer machine were used for assessment before and after sliding. Frictional forces values during sliding were as follows in descending order; Inspire ICE™, CLEAR™, DISCREET™, Symetri Clear™, and, lastly, Victory™. Also, DISCREET™ scored the highest in surface roughness (Sa) values followed by Symetri Clear™. None of the correlations were statistically significant. Frictional forces produced during sliding were not always directly related to surface roughness. Monocrystalline ceramic brackets appeared to have the greatest FF and a low surface roughness. Furthermore, DISCREET™ scored a very low frictional value comparable to metal brackets yet showed the highest surface roughness. Metal brackets exhibited the greatest surface smoothness before sliding and the least SF. Predicting the FFs produced during sliding mechanics would help the practitioner while choosing the bracket system to be used, and while planning the treatment mechanics, how much force to deliver, and how much tooth movement to expect. How to cite this article: AlBadr AH, Talic NF. Correlating Frictional Forces Generated by Different Bracket Types during Sliding and Surface Topography Using Scanning Electron Microscopy and Optical Profilometer. J Contemp Dent Pract 2024;25(1):41-51.

Simultaneously Improving the Strength and Plasticity of Additively Manufactured 316L Stainless Steel by Adding Aluminum

Due to the special layer‐by‐layer printing process of additive manufacturing (AM), the heat dissipation in the printed material tends to flow mainly along the building direction, which results in the formation of coarse columnar grains in AM metals. The coarse grains are detrimental to the mechanical properties of AM metals, and are not conducive to the lightweight development of AM metal components. This article proposes a printing strategy for adding aluminum to 316L stainless steel. Based on the aluminum‐reinforced strategy, low melting point MnSiO3 particles are transformed into high melting point Al‐containing particles (such as Al2O3), and the grain size of 316L stainless steel produced by direct energy deposition (DED) is refined, resulting in a significant improvement of tensile strength. What is more, the increase in tensile strength of Al‐reinforced 316L does not sacrifice its plasticity. Attributed to the twinning‐induced plasticity effect and good adhesion between Al2O3 particles and matrix, the plasticity of Al‐reinforced 316L is synchronously improved. To be more specific, compared to DED‐316L without adding Al, the yield strength and tensile strength of samples with adding 0.5%wt Al are individually improved by 14.8% and 16.2%; at same time, the uniform elongation and total elongation are increased by 80.4% and 13%, respectively. The printing strategy proposed in this article is expected to provide reference for the strengthening and toughening of AM metals, thereby contributing to the lightweight development of AM components.

The specific heat of superconducting metallic grains in magnetic field

More and more studies indicate that the effects of quantum size and energy level statistics play a crucial role in the thermodynamic properties of ultrasmall metallic grains. This paper aims to investigate how they affect the specific heat of ultrasmall metallic grains in magnetic field. As the particle size decreases, fluctuation effects and the impact of energy level separation are becoming more and more important. The method of static path approximation (SPA) is adopted to handle the fluctuation effect. Random matrix theory (RMT) is adopted due to its successful description of the energy level of metal nanoparticles. The normalized specific heat of several typical temperatures and electron spins were taken in the calculation, and the results were analyzed. It was found that spin and the spin-orbit coupling affect the specific heat very obviously, and the suppressed high spin weakens the contribution of electrons to the heat capacity.

A Relevant Characterization and Compatibility for Reuse the Sediments from Reservoirs in Southern Italy

The damming of watercourses results in sediment accumulation and, therefore, in the reduction of useful storage capacity. The storage capacity can be recovered through dredging, but this process generates large volumes of sediments that require proper management. To avoid landfilling and promote recovery operations, sediment characterization is the preliminary step to any assessment and decision. This paper presents the results of tests on sediments sampled at two reservoirs in southern Italy, the Camastra and the San Giuliano, in Basilicata. These investigations include testing of organic matter, heavy metals grain size distribution, and the assessment of the pollution degree. A lack of correlation between the sampling point and the heavy metal content was observed in sediments, except Be, Cr and Ni for the San Giuliano reservoir. This may be attributed to the presence of agricultural activities and fertilizer use in its watershed. Similarly, there is no dependence between the organic carbon and the grain size distribution, the former being scarcely found in both reservoirs (on average 0.91% for the Camastra sediments and 0.38% for the San Giuliano sediments), the latter being predominantly characterized by sandy matrices downstream of the reservoirs (on average 64.3% ± 32.9%) and by silty-clayey matrices in the upstream areas (on average 65% ± 14.3%). Finally, the determination of the single pollution index Pi and the Nemerow integrated pollution index PN highlights that sediments are not contaminated with heavy metals. Most of them show values of the indices above between 0 and 1 (“unpolluted”) and, in a few cases, values between 1 and 2 (“poorly polluted”). The findings suggest that these sediments can be reused for environmental and material recovery, using them as secondary raw materials for sub-bases and embankments, for filling in disused quarries, for reprofiling and reconstructing the morphology of coastlines or riverbeds, for beach nourishment and in the agronomic and construction industry fields.

Hierarchical structure of poly(ε-caprolactone) crystals on its copolymer poly(l-lactide-co-ε-caprolactone) fibers

In crystallization, heterogeneous structures of copolymers are employed to establish a hierarchical architecture comprising two polymers, this typically occurs on the surface of block copolymers or blended polymers. While hierarchical structures in block copolymer fibers are well-established and widely utilized, achieving a regular hierarchical structure on random copolymer fibers is both meaningful and challenging. Here, we present a case of forming a hierarchical structure on the surface of the random copolymer poly(L-lactide-co-caprolactone) (PLCL)fibers. The (ε-caprolactone)(CL) polymer chain segments of the random copolymer are released on the surface of the modified copolymer fiber using sodium hydroxide. Subsequently, poly(ε-caprolactone)(PCL) forms a shish kebab-like crystalline structure under the guidance of the CL segments. The CL segments act as crystalline precursors to induce the formation of heterogeneous PLCL/PCL shish kebab structures. The variation of CL segments on the fiber changes with modification time, leading to the formation of crystalline lamellae of different sizes, which had been confirmed by characterization techniques such as scanning electron microscope (SEM), 1H NMR, X-ray photoelectron spectra (XPS), differential scanning calorimetry (DSC), etc. The implementation of this heterogeneous structure provides possibilities for the implementation of hierarchical structure in random copolymers.

The study of grain transport effects on grain refinement under pulsed magnetic fields

The motion of grains within the molten metal under a pulsed magnetic field influences the influx of grains, thereby impacting the refinement of the solidification structure of metal. Physical simulation experiments, solidification studies, numerical simulations, and theoretical analyses are combined to investigate the motion patterns of grains in molten metal subjected to a pulsed magnetic field in the case of identical power. The findings suggest that grain movement occurs in two primary phases: initially, within the non-flow area at the solid-liquid interface, where grains respond to electromagnetic forces, and subsequently, within the flow area where the molten metal carries the grains. The speed of grain transport in the flow area directly influences the movement of grains in the non-flow area, then affecting the refinement of the metal solidification structure. The study introduces the concept of "transport characteristic time" to quantify the transport capacity of grains within the flow area, which enables a quantitative analysis of refinement effect under identical power conditions.

Assessment of the metal grain size of 12Cr1MoV steel by LIBS coupled with acoustic wave information

A modelling scheme that integrates spectral and acoustic data was put forth as a means of enhancing the precision of grain size detection in 12Cr1MoV steel.

Observation of Vacuoles in Arabidopsis Developing Pollen Grains with Whole-Cell Electron Tomography.

Arabidopsis thaliana developing pollen grains serve as an excellent system for studying vacuole dynamics. Here, we present a methodological approach that utilizes the serial tomography package in Etomo software from IMOD to generate whole-cell tomograms on A. thaliana developing pollens for visualizing vacuoles on the whole-cell scale. In order to understand the vacuole dynamics along with the pollen maturation, we also introduce a sampling method aimed at harvesting the pollen grains at various stages, marked by the vegetative nucleus or generative cell. The cryo-fixation/freeze-substitution technique can then be applied to preserve the fine structures of the pollen grains and facilitate detailed ultrastructure examination. Through this method, large-volume whole-cell electron tomograms regarding vacuolar morphologies and ultrastructural changes during pollen development and maturation have been obtained. Overall, the method presented here provides valuable insights into the dynamic nature of vacuoles in Arabidopsis developing pollen.

Preferential formation of the stereocomplex crystals of poly(L‐lactide) and poly(D‐lactide) blend by epoxidized soybean oil under nonisothermal crystallization

AbstractFormation of stereocomplex crystals (SCs) in enantiomeric poly(L‐lactide) (PLLA) and poly(D‐lactide) (PDLA) blends is an effective way to improve the heat resistance and mechanical performance of polylactide (PLA) products. However, obtaining PLAs with high stereocomplex content is not straightforward as the homocrystal and SCs occur simultaneously and compete with one another. In this work, various amounts of epoxidized soybean oil (SO) or SO at 3%–20% by weight were added to equal amounts of the stereoisomers (PLLA/PDLA; 50/50). From differential scanning calorimetry, it was found that epoxidized SO increased the crystallization temperature, facilitated the SC crystallization, and suppressed the homecrystal formation, whereas SO did not affect the crystallization behavior for the racemic blends. Moreover, epoxidized SO reduced the glass transition temperature, cold crystallization temperature, and melting temperature of the racemic blends. We examined how epoxidized SO affected the crystallization of PLLA/PDLA at cooling rates from 2 to 20°C/min. We discovered that epoxidized SO still encouraged SC crystallization. The activation energy, calculated from Takhor and Kissinger equations, indicated that adding 5 wt% epoxidized SO effectively promoted the crystallization and facilitated the SC formation of the PLLA/PDLA blend.

Transformation of poly(l-lactide) crystals composed of linear chains into crystals composed of cycles

A poly(l-lactide) with a trifluoro ethyl ester end group and an average degree of polymerization (DP) of 50 was synthesized by ROP of l-lactide initiated with trifluoroethanol.

(Invited) Investigating Microstructural Effects of Composite NCM811 Cathodes on ALL-Solid-State Li-Ion Batteries Performance Under Low Operation Stacking Pressure

All-solid-state lithium-ion batteries (ASSLIBs) have been considered suitable alternatives to commercial lithium-ion batteries (LIBs) in the aspect of safety issues that come from the use of inflammable solid electrolytes to replace organic flammable electrolytes. Nevertheless, there apparently remains much room for a better understanding of their properties and behaviors in order to upgrade their performance to reach the practical application level. Ni-rich layered oxides, LiNi1-x-yCoxMnyO2 (NCM), are promising cathodes for high-energy ASSLIBs because of their high capacities and redox potentials, and low material cost when compared with conventional LiCoO2. However, certain challenges associated with their use in ASSLIBs must be addressed for their effective use and industrialization. In particular, the structural integrity of the NCM electrodes during the long-term charge/discharge process suffers from the formation of an intergranular and/or intragranular cracking behavior. These microcracks are initiated at the grain boundaries from the anisotropic chemical strain of the randomly oriented polycrystal (PC) primary cathode particles. Solid evidence behind the electrochem-mechanical breakdown of an NCM cathode with liquid electrolytes has been well discussed and reported in the literature. However, the breakdown in ASSLIBs may not obey as same as in the liquid-electrolyte LIBs and display exclusive mechanics-oriented material damage in the presence of rigid solid-state electrolytes (SSEs). The primary objective of this research is to gain a deeper understanding of various cracking modes in ASSLIBs, which we believe is instrumental to improving the lifespan and cell performance as a whole. ForASSLIBs, stacking pressures greater than 100 MPa under battery operation are currently commonly used. The use of high stacking pressure increases manufacturing and usage difficulties and overall cost. Lowering the battery-operation stacking pressure, for example to the level of the liquid-electrolyte batteries, will certainly facilitate the wider applications of ASSLIBs. In this context, composite cathodes consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and brittle Li3InCl6 (LIC) SSE have been assessed for ASSLIB applications under low operation stacking pressure (coin-cell configuration; ~2.0 MPa). The study reveals the effects of material and structural characteristics of the composite cathode, including the NCM particle size and size distribution, active-material spatial distribution, particle crystallinity (polycrystal or single-crystal), and electrochemical operation parameters (voltage range, current rates) on the cycle stability of the ASSLIBs as a result of the electrochem-mechanical behaviors of the oxide cathode. Meanwhile, a novel solvent-based synthesis process of LIC for achieving high-density cathodes is introduced.

First classification of iron meteorite fragment preserved in Chang’e-5 lunar soils

Lunar soil preserves numerous fragments of meteorites impacting on the Moon, providing a unique opportunity to investigate the distribution of the types of projectiles over billions of years. Here we report the first discovery of an iron meteorite fragment from the Chang’e-5 lunar soil, which consists mainly of martensite (quenched from taenite), kamacite, and schreibersite, with a trace of pentlandite. The meteorite fragment is Ni- and P-rich, S-poor, and based on its mineral chemistry and bulk composition, can be classified into the IID-group, a rare and carbonaceous group of iron meteorite originating in the outer Solar System. This meteorite fragment experienced only limited partial melting followed by fast cooling, suggestive of efficient preservation of intact remnants of iron meteorites impacting on the porous lunar regolith. Alternatively, it is a relic of a low-velocity impact of submillimeter-sized metal grains originated from an IID-like iron meteorite. Our observations demonstrate that it is feasible to achieve the type distribution of meteorites impacting on the Moon via systematically analyzing a large number of metal grains separated from lunar soils, thus shedding light on the dynamic evolution of the Solar System.

STRUCTURAL CHANGES IN CdTe SINGLE CRYSTALS UPON IRRADIATION WITH HEAVY IONS OF INDERENT GASES

The paper presents the results of studies on the production of a polycrystalline or amorphous layer by irradiation of single-crystalline cadmium telluride with ions of inert gases differing in radii. The influence of the ion radius on the resistivity and structure of the (111) layer of a single crystal of cadmium telluride has been studied. The samples were irradiated with neon, argon and xenon ions with radii of 38, 71 and 108 picometers (10-12 m), respectively. The radiation dose for all ions was 250 Mrad. It has been shown that ions with a large radius have the strongest influence on structural transformations; at the same dose (250 Mrad), the drop in intensity of the (111) reflection under the influence of xenon ions is twice as high as that of neon ions. In accordance with X-ray data, as the radius of the ion increases, the resistivity increases, and the larger the radius of the ion, the greater the rate of increase r. Irradiation transforms a single crystal into a polycrystalline state with the formation of a large number of defects, which are sources of current carrier capture, which leads to an increase in r. The increasing growth of r with increasing ion radius is apparently due to the fact that ions with a larger radius have a significantly larger effective cross section for interaction with the crystal.

Liquid crystalline composite hydrogels with large pH-triggered anisotropic swelling for embolotherapy

Inspired by the anisotropic structure of biological tissues, anisotropic hydrogels have been developed using various nanofillers, however, it remains a big challenge to synthesize hydrogels with large swelling anisotropy. Herein a single molecule filler, α-helical polypeptide, instead of nanoscale fillers, was used to synthesize anisotropic hydrogels. First nematic liquid crystal of poly(γ-benzyl l-glutamate) (PBLG) was prepared by shearing and stabilized by embedding in a crosslinked polymer matrix. The resulting PBLG composite gels were then converted to poly(L-glutamic acid) (PLGA) composite gels by debenzylation. The rigid rod-like structure of α-helical PBLG chains makes them easy to be orientated. The pH-sensitivity of PLGA makes the resulting composite gels pH-sensitive without the need to couple with a stimuli-responsive hydrogel matrix. In response to pH change PLGA composite gels swell anisotropically with a much larger swelling degree in the radial direction than in the axial direction. The swelling anisotropy (3.43) is much higher than most anisotropic hydrogels, particularly the stimuli-responsive ones reported previously. The composite gel also exhibits anisotropic mechanical properties with a larger Young's modulus in the axial direction than that in the radial direction. Preliminary test demonstrated that the composite gels have potential in embolotherapy thanks to its large pH-triggered anisotropic swelling. Statement of SignificanceAnisotropic hydrogels have important biomedical applications. Introduction of oriented nanofillers has been demonstrated a popular and versatile method for their synthesis, however, it remains a big challenge to achieve large swelling anisotropy. Herein a single molecule filler, α-helical polypeptide, instead of nanoscale fillers, was used to synthesize anisotropic hydrogels. This filler can be easily oriented by shearing. More importantly, as single molecule filler, it can constrain the swelling of hydrogel matrix more effectively. Using this filler, a pH-sensitive hydrogel with large swelling anisotropy (3.43) was successfully synthesized. Thanks to its large pH-triggered anisotropic swelling the hydrogel was successfully used as embolic agent to occlude vessels.

Microstructure, dielectric and optical properties of transparent flexible high-k Bi1.5MgNb1.5O7 thin films

High-k insulation materials can effectively reduce the operating voltage and leakage current of TFT devices, improving device performance owing to their high dielectric constant and insulation properties. Transparent flexible Bi1.5MgNb1.5O7 (BMN) dielectric thin films were synthesized via RF magnetron sputtering at room temperature. The impact of argon to oxygen ratio (Ar:O2) on the microstructure, elemental composition, optical, and dielectric properties of the BMN dielectric films was systematically explored. X-ray photoelectron spectroscopy, scanning electron microscopy, and optical property tests revealed that the proportion of metallic Bi and grain size play crucial roles in the optical transmittance and optical bandgap of the BMN films. Moreover, the dielectric properties were significantly influenced by the space charge polarization resulting from the percolation capacitance model formed by metallic Bi in the samples. To further optimize the dielectric properties of BMN films, sandwich structured OAO (BMNO/BMNAr/BMNO) composite films were designed. The OAO composite film exhibited the best overall performance, with an average transmittance of 92.27 %, a dielectric constant of 84, a dielectric loss of 0.00672, and a leakage current density of approximately 1.4 × 10−8 (5 V) when the thickness of the BMNO layer was 15 nm. These results highlight the significant potential of BMN as a transparent flexible high-k dielectric material.

Understanding the Poly (Triazine Imide) Crystals Formation Process: The Conversion from Heptazine to Triazine.

Poly (triazine imide) (PTI) generally obtained via ionothermal synthesis features extended π-conjugation and enhanced crystallinity. However, in-depth investigation of the polycondensation process for PTI is an onerous task due to multiple influencing factors and limited characterization techniques. Herein, to simplify the polymerization route and exclude non-essential factors, PTI was prepared by calcining only melamine and LiCl. This study aims to identify the pivotal role of LiCl in PTI formation, which can convert heptazine-based intermediates into more stable triazine-based PTI framework. Based on this discovery, we demonstrate the transformation process of the prepared samples from amorphous Bulk g-C3 N4 to regular PTI, and further prove that the reaction with LiCl causes disruption of heptazine covalent organic frameworks. Additionally, the PTI exhibits higher photocatalytic water splitting performance due to efficient charge carrier mobility and separation, as well as faster reaction kinetics. This discovery deepens understanding of the polycondensation process of PTI crystals and provides insights toward the rational design of crystalline carbon nitride-based semiconductors.

Electrochemical Activation of Ordered Mesoporous Solid Electrolyte Interphases to Enable Ultra‐Stable Lithium Metal Batteries

AbstractIn Li metal batteries, the rational construction of artificial solid electrolyte interphase (ASEI) can homogenize the Li‐ion flowing and Li‐mass plating/stripping, and reinforce the mechanical and electrochemical stabilities of electrode–electrolyte interface. Here, an ordered‐mesoporous powder zirconium oxophosphate (ZrOP) is proposed to construct a Li‐ion conductive ASEI by brushing ZrOP on metallic Li. The P‐induced amorphization in ZrOP is expected to accelerate the spontaneous lithiation reaction and promote the generation of P‐contained Li‐ion conductors and LiF domains in ASEI during Li anode cycling. The electrochemical activation of ASEI with promoted ionic conductivity and interconnected porous network is favorable for the homogeneous nucleation and growth of Li metal grains (with ≈10 µm in size), and the suppression of Li dendrites and volume expansion during long‐term Li plating and stripping. The ZrOP‐modified Li symmetric cell enables a long lifespan of over 1600 h at 1 mA cm−2, and the corresponding LiNi0.8Co0.1Mn0.1O2 (NCM811) based full cell displays a stable cycling for at least 300 cycles with a capacity retention of 80% at 1 C. The modified thin Li foil (40 µm in thickness) anode also enables a multilayered pouch cell based on a high‐loading NCM811 cathode with stable cycling and reversible capacity over 1 Ah.

Phase and defect diagrams based on spectral grain boundary segregation: A regular solution approach

Recent works have proposed the treatment of alloy defect states with thermodynamics analogous to phase thermodynamics, so they can be analyzed in a manner that is comparable to bulk phase diagrams. We refer to such diagrams containing both bulk phase and defect state information as “phase-and-defect diagrams.” Segregated grain boundaries (GBs) are an example of one such defect state, which enable, for example, the stabilization of nanocrystalline alloys. The recent development of spectral thermodynamic isotherms has demonstrated that a fully spectral description, which captures the complete distribution of local atomic environments in the grain boundary network, is necessary for accurate modeling of segregation behavior. To our knowledge, there is currently no spectral free energy formulation from which a phase-and-defect diagram of the segregated polycrystalline state can be produced. In this work, we present a spectral regular solution model of grain boundary segregation, from which we derive an analytical free energy function for the segregated polycrystalline state. We then use this free energy representation to construct a phase-and-defect diagram for a hypothetical alloy system, providing a framework for future efforts in developing spectral phase-and-defect diagrams.

Sample size effects on the critical state shear strength of granular materials with varied gradation and the role of column-like local structures

Assessing the shear strength of coarse granular soils is challenging because testing devices in the laboratory often limit the maximum particle size (dmax). Although engineering standards define representative elementary volumes (REVs) using the aspect ratio α = X/dmax, where X is the characteristic sample size, they often disagree on the minimum α, as the effects of sample scale on shear strength are still not well understood. This paper presents a discrete-element study on the combined effect of specimen size and grading on the critical state shear strength of granular materials. The study covers a wide range of aspect ratios and demonstrates that the macroscopic response is stable for α ≥ 15 – which is significantly higher than the standard requirement of α ≥ 10 for simple shear tests. The granular microstructure is also strongly affected by α and the formation of column-like structures of grains carrying strong contact forces, reaching sample size independent conditions only for α ≥ 20. Such column-like structures are shown to be primarily composed of the largest classes of grains, supporting the fact that grading has no effect on the critical state shear strength and dmax correctly serves to scale a granular sample to the size of the testing device.

Grain Crystallinity, Anisotropy, and Boundaries Govern Microscale Hydrodynamic Transport in Semicrystalline Porous Media.

Polycrystallinity is often an unintended consequence of real manufacturing processes used to produce designer porous media with deterministic and periodic architectures. Porous media are widely employed as high-surface conduits for fluid transport; unfortunately, even small concentrations of defects in the long-range order become the dominant impediment to hydrodynamic transport. In this study, we isolate the effects of these defects using a microfluidic analogy to energy transport in atomic polycrystals by directly tracking capillary transport through polycrystalline inverse opals. We reveal─using high-fidelity florescent microscopy─the boundary-limited nature of flow motions, along with nonlinear impedance elements introduced by the presence of "grain boundaries" that are separating the well-ordered "crystalline grains". Coupled crystallinity, anisotropy, and linear defect density contribute to direction-dominated flow characteristics in a discretized manner rather than traditional diffusive-like flow patterns. Separating individual crystal grains' transport properties from polycrystals along with new probabilistic data sets enables demonstrating statistical predictive models. These results provide fundamental insight into transport phenomena in (poly)crystalline porous media beyond the deterministic properties of an idealized unit cell and bridge the gap between engineering models and the ubiquitous imperfections found in manufactured porous materials.