Amorphous Part Research Articles

Electrolyte exposure time effects on structure, composition and biocompatibility of microarc oxidation coatings on Mg-Ca-Zn alloys

The problem of using magnesium in medicine is biodegradation, which leads to the loss of the implant mechanical integrity before the bone tissue formation. Doping and subsequent coating deposition is an effective solution to this problem. This paper investigates the effects of electrolyte exposure time during micro-arc oxidation of the Mg-Ca-Zn alloy on its phase composition, biodegradation, and biocompatibility. As a result of micro-arc oxidation, a dense coating with a gradient structure is formed on the surface of the Mg-Ca-Zn alloy, consisting of amorphous and amorphous-nanocrystalline parts. The amorphous layers of the coating mainly consist of O, P, and Mg. The nanocrystalline layer is enriched in F, while the diffusion zone is enriched in O, F, and Mg. The coating has a porous structure typical for microarc oxidation. The nonlinear behavior of the diffraction pattern at small diffraction angles indicates the amorphous state of the coating. The amount of amorphous component is increasing with exposure time, indicating an increase in the coating thickness. Scratch testing with a diamond indenter tip indicates good coating adhesion. All coated Mg-Ca-Zn samples show a significant reduction in weight loss compared to the uncoated sample after 21 days in the culture medium. Surgical treatment of rabbit femurs with implants made from coated Mg-Ca-Zn samples demonstrated high biocompatibility. Clinical evaluation of the results showed a complete absence of purulent-inflammatory complications in all animals during the first 28 days after implantation.

Free volume can control biodegradation rate of polylactic acid

We evaluated whether the enzymatic degradation rate of biodegradable plastics is related to the amorphous structure of the polymer. The “free-volume,” meaning the cavity between the polymer chains in the amorphous part, is known to influence various physical properties. In this study, enzymatic degradation tests were performed on polylactic acid (PLA) films with free-volume hole sizes estimated by positron annihilation lifetime spectroscopy (PALS). Films with different free-volume hole sizes near the surface region degraded in different modes, and a positive correlation, with a correlation coefficient of 0.713, was observed between the degradation rate in the initial 30 min and the free volume size near the surface. These results suggest the possibility of controlling the degradation rate of the amorphous region by controlling the free volume size, which is important for future applications of biodegradable plastics in a wide range of fields.

Separation of amorphous and semicrystalline parts of LLDPE with high‐temperature interactive liquid chromatography

AbstractLinear low‐density polyethylene (LLDPE) materials may contain components, which are soluble at room temperature. These may influence physical properties or raise concerns for end‐users and regulatory bodies because LLDPE is widely used for food packaging. Due to the nonpolar and amorphous nature of the room temperature soluble part of LLDPE, its molecular characterization with common methods for polyolefin analysis, such as Temperature Rising Elution Fractionation (TREF), Crystallization Fractionation (CRYSTAF), or Differential Scanning Calorimetry (DSC), has proven to be very challenging. Separation of the amorphous part of LLDPE, as well as its semicrystalline part, is, however, realizable with high‐temperature liquid chromatography (HT‐LC), which is demonstrated for the first time in this work. This technique enables to evaluate the chemical composition distribution of the room‐temperature solubles and non‐solubles in LLDPE samples. It was found that LLDPE synthesized with metallocene catalysts contained only a very small amount of amorphous material. In contrast, LLDPE prepared with Ziegler‐Natta catalysts contained up to 14 wt.% of the amorphous copolymer. The latter was soluble at room temperature, had a weight‐average molar mass ranging from 60 to 200 kg/mol, and contained about 10 mol% more 1‐olefin than the non‐soluble part of LLDPE.

Nucleation During Storage Impeded Supersaturation in the Dissolution Process of Amorphous Celecoxib.

The aqueous solubility of active pharmaceutical ingredients (APIs) is one of the most critical factors in determining the absorption of orally administered drugs. Amorphization of API may offer better drug absorption than the crystalline state owing to enhanced solubility. However, if crystal nuclei are formed during storage, they may develop into crystals upon contact with water, thus limiting the dissolution advantage. In an earlier study, we found that the nuclei of amorphous celecoxib (CEL) could be formed at freezing temperatures (FT) without further crystal growth. Following this finding, we compared the dissolution performances of amorphous CEL annealed at room temperature (RT, 25 °C) or FT (-20 °C). We found that only the RT-annealed CEL could achieve a supersaturated state effectively during the dissolution process, which could be explained by the fast conversion of the FT-annealed amorphous CEL to a crystalline state owing to the presence of nuclei. Investigation of the residual solids revealed that supersaturation could be maintained for a while after the appearance of the crystals, which could be explained by heterogeneous nucleation and competition between the dissolution of amorphous parts and crystallization. In addition, a new crystalline form of CEL was observed during dissolution.

Crystal formation in Eu3+ - Doped oxyfluorophosphate glass-ceramics for luminescence thermometry

Eu3+ doped-Oxyfluorophosphate glasses with a general composition 75 NaPO3 - (25-x) CaO – x CaF2 (with x ranging from 0 to 25 mol%) were prepared and their spectroscopic changes induced by the addition of fluorine and when applying a thermal treatment in order to grow crystals in the glasses were investigated. The addition of CaF2 at the expense of CaO reduces Ω2 and Ω4 parameters indicating that the Eu3+ ions are located in less covalent and well separated sites in oxyfluorophosphate glasses. An increase in the CaF2 content at the expense of CaO also leads to an increase in the absolute thermometric sensitivity from (4.2 × 10−4) K−1 to (17.6 × 10−4) K−1 at 523 K while decreasing the relative thermometric sensitivity from 3.0% to 1.4%.The heat treatment leads to the precipitation of crystals, the composition of crystal phase depends on the glass composition. For the glasses with x = 0 and 10, the thermal treatment increases Ω6 while reducing Ω4, as a result of an enhanced stiffness and reduced covalency of dopant's environment due to the precipitation of various crystals. As Ω2 remains unchanged, the Eu3+ are suspected to remain mainly in the amorphous part of the glass-ceramics in agreement with the lack of sharp peaks in the emission spectrum. For the glasses with x = 20 and 25, Ω2 increases indicating a change in the site symmetry of Eu3+ resulting from the dopant entering the CaF2 crystalline phase. Due to the changes in the Eu3+ sites in the heat treated glasses, the heat treatment of the glass increases the absolute thermal sensitivity, but reduces the relative thermal sensitivity. The oxyfluorophosphate glass-ceramic with x = 25 exhibits high absolute thermometric sensitivity compared to oxyfluorophosphate glass, but also comparatively low relative sensitivity of 0.5% K−1.

Influence of oxygen in the production chain of Cu–Ti-based metallic glasses via laser powder bed fusion

ABSTRACT Laser powder bed fusion of metals (PBF-LB/M) is advantageous for manufacturing bulk metallic glasses with size and geometrical freedom. However, the oxygen uptake along the production chain can negatively impact the generation of high-quality, amorphous parts. In this context, Cu–Ti-based alloys were gas-atomised and additively manufactured using commercial- (CP) and high-purity (HP) feedstocks. The oxygen absorption in each processing step was tracked and related to the amorphous phase formation and glass-forming ability (GFA) of alloys. Results show an increasing oxygen absorption, considerably influenced by the starting feedstock, especially for CP. In HP material, the most contribution is inherent from the powder oxygen content. Results reveal the lack of influence of the oxygen content in the GFA. TEM analysis of commercial powder and PBF-LB/M sample show uniform and featureless micrographs, displaying the absence of oxygen-induced nucleation. The present contribution enhances the qualification and economic processability of amorphous metals by PBF-LB/M.

Surface modification of the Nylon 6,6 and wasted glass fiber‐Nylon 6.6 coatings using atmospheric plasma treatment

AbstractPolymers tend to have low surface free energy, a significant cause of adhesion properties with other substances. Plasma treatment is an optimal method to improve surface properties. This work used a recycled glass fiber‐polymer coating, and another based on Nylon 6,6. The surface modification of both layers was carried out with an atmospheric plasma treatment at different times. Chemical analysis of the plasma treated and the untreated surface were analyzed by infrared spectroscopy and X‐ray diffraction. Atomic force microscopy (AFM) investigated the morphology and topography surface. The plasma treatment results improve wettability and surface free energy. The contact angle decreases for Nylon 6,6 from 68° to 0° and for glass fiber‐polymer from 56° to 18°. However, the wettability remains over time in Nylon 6,6 layer, and the composite material reverts in 15 days. The high surface free energy after plasma treatment was mainly due to an increase in the polar component by inserting polar groups. The % crystallinity increases with plasma treatment due to the loss of the amorphous part of the polymer by plasma etching. AFM analysis shows an improvement in the roughness surface after treatment. These results greatly interest in enhancing adhesion with other substrates.

Plasticity and brittleness of Fe-based amorphous alloy strips assessed via a single abrasive impact method

Fe-based soft magnetic amorphous alloys represent the next generation of magnetic core materials and are expected to replace silicon steel sheets in many applications. An economical and fast methodology for the study of the plasticity and brittleness of this material is however necessary to permit its widespread use. Abrasive water jetting is a cold processing technique that has great potential for use in the fabrication and inspection of Fe-based amorphous alloy parts. However, research on this technique is currently lacking. In order to assess the plasticity and brittleness of Fe-based amorphous alloys by considering abrasive impacts, this work investigates the effect of impact speed and impact angle on the removal process in Fe-based amorphous alloys and establishes the corresponding abrasive erosion mechanism. It is found that Fe-based amorphous alloys exhibit four primary responses: shear slip, viscous flow, shear crack formation, and brittle fracture; the plasticity and brittleness of Fe-based amorphous alloys are assessed by considering the impact morphology and mechanism.

The effects of thermal annealing on the performance of material extrusion 3D printed polymer parts

This article presents the effects of thermal annealing at elevated temperatures (> glass transition temperature Tg) on the performance of polymer parts via material extrusion 3D printing. Both semi-crystalline and amorphous filaments were used. As-printed parts were designed to be amorphous and then annealed at 60, 110 and 150 °C for different durations ranging from 50 to 6400 s. The flexural strength and Young’s modulus increased by a maximum of approximately 10%. The increase was ascribed to crystallisation development during annealing, as confirmed by thermal and morphology characterisations. Hence, this effect was only observed with semi-crystalline materials. On the other hand, all the annealed parts expanded in the thickness direction and shrank in the perpendicular plane. The maximum linear strain reached 20%, while the volume strain was negligible. These morphology changes after annealing reversed the strain-hardening of the strand and led to inferior strand performance against local tensile deformation. The degradation can outweigh the benefits of crystallinity development. For amorphous parts, the degradation reached approximately 25% in both the flexural strength and the modulus.

Layer thickness dependent plastic deformation mechanism in Ti/TiCu dual-phase nano-laminates

Crystalline/amorphous nanolaminate is an effective strategy to improve the mechanical properties of metallic materials, but the underlying deformation mechanism is still under the way of exploring. Here, the mechanical properties and plastic deformation mechanism of Ti/TiCu dual-phase nanolaminates (DPNLs) with different layer thicknesses are investigated using molecular dynamics simulations. The results indicate that the influence of the layer thickness on the plastic deformation mechanism in crystalline layer is negligible, while it affects the plastic deformation mechanism of amorphous layers distinctly. The crystallization of amorphous TiCu is exhibited in amorphous parts of the Ti/TiCu DPNLs, which is inversely proportional to the layer thickness. It is observed that the crystallization of the amorphous TiCu is a process driven by stress and heat. Young’s moduli for the Ti/TiCu DPNLs are higher than those of composite material due to the amorphous/crystalline interfaces. Furthermore, the main plastic deformation mechanism in crystalline part: grain reorientation, transformation from hexagonal-close-packed-Ti to face-centered cubic-Ti and body-centered cubic-Ti, has also been displayed in the present work. The results may provide a guideline for design of high-performance Ti and its alloy.

Evaluation of the Equilibrium Melting Temperature and Melting Behavior of Poly(Phenylene Sulfide) Crystals.

Focusing on the melting process of poly(phenylene sulfide) (PPS) crystals, one of the high-performance resins with a very wide range of applications, we attempted to clarify the melting process and derive the equilibrium melting temperature with structural analysis using X-ray scattering and thermal measurements. Two melting points were observed in the crystallized PPS films by DSC measurements. We focused on the low-temperature melting point, in situ small-angle and wide-angle X-ray scattering measurements using synchrotron radiation and DSC thermograms indicate the melting of microcrystals because of thickening of the amorphous part from small-angle X-ray scattering results. In addition, the Hoffman-Weeks plot based on the results of fast scanning calorimetry showed that the melting temperature is almost parallel to the straight line where melting temperature and crystallization temperature are equal, indicating that the melting is of a metastable structure. The melting point on the high temperature side was attributed to the melting of lamellar crystals. The equilibrium melting point was derived from the Hoffman-Week and Gibbs-Thomson plots as 318 °C.

Impact of Silica-Modification and Oxidation on the Crystal Structure of Magnetite Nanoparticles

At present, the widespread use of iron oxide nanoparticles, including for commercial purposes, requires strict preservation of their phase composition during their application. The choice of nanoparticle modifier and modification conditions is decisive due to their high sensitivity to oxygen in the case of using real conditions (O2, pH change, etc.). In this work, we studied the change in the phase composition of magnetite nanoparticles after modification with 3-aminopropyltriethoxysilane (APTES) and oxidation with nitric acid in order to estimate the protective potential of the silica shell. After modification by APTES and oxidation with nitric acid, the nonstoichiometric nature of the magnetite nanoparticles according to XRD data increased, which indicates an increase in transition forms compared to the initial sample (magnetite content decreased to 27% and 24%, respectively). In contrast, Mössbauer spectroscopy data detected a decrease in the nonstoichiometric index due to APTES modification conditions, but strong oxidation after exposure to nitric acid. It also showed that by analyzing the data of the diffraction analysis and Mössbauer spectroscopy for the same sample, one can obtain information not only about the ionic composition of “magnetite”, but also about the distribution of iron ions of different charges over the crystalline and amorphous parts of the preparation.

Development of phytoglycogen-derived core-shell-corona nanoparticles complexed with conjugated linoleic acid.

Phytoglycogen-derived self-assembled nanoparticles (SMPG/CLA) and enzymatic-assembled nanoparticles (EMPG/CLA) were fabricated for delivery of conjugated linoleic acid (CLA). After measuring the loading rate and yield, the optimal ratio for both assembled host-guest complexes was 1 : 10, and the maximum loading rate and yield for EMPG/CLA were 1.6% and 88.1%, respectively, higher than those of SMPG/CLA. Structural characterization studies showed that the assembled inclusion complexes were successfully constructed, and had a specific spatial architecture with inner-core amorphous and external-shell crystalline parts. A higher protective effect against oxidation of EMPG/CLA was observed than that of SMPG/CLA, supporting efficient complexation for a higher order crystalline structure. After 1 h of gastrointestinal digestion under the simulated conditions, 58.7% of CLA was released from EMPG/CLA, which was lower than that released from SMPG/CLA (73.8%). These results indicated that in situ enzymatic-assembled phytoglycogen-derived nanoparticles might be a promising carrier platform for protection and targeted delivery of hydrophobic bioactive ingredients.

Structural characterization and stability of microencapsulated flavonoids from Lycium barbarum L. leaves

Lycium barbarum L. leaves are rich in flavonoids, which have been proven to show poor stability and solubility in the external and gastrointestinal environment. To improve the stability and water-solubility of Lycium barbarum L. leaves flavonoids (LBLF), sodium alginate (SA) and chitosan (CS) were utilized as the wall materials to prepare the microcapsules of LBLF (M-LBLF) by polyelectrolyte cross-linking method. The spectrum of Fourier Transform Infrared spectroscopy (FT-IR) showed M-LBLF had an absorption peak at 1735 cm-1, which might be the electrostatic interaction between the positive and negative charges of SA and CS. X-ray diffraction (XRD) spectrum showed the diffraction peak at 2θ = 51.8° was due to the microencapsulation and transformation of the amorphous structural part into a crystalline state. As demonstrated by Differential Scanning Calorimetry (DSC), the M-LBLF displayed wider and higher endothermic peaks due to the electrostatic interaction between SA and CS. The release of main monomers from M-LBLF in different stages of the in vitro digestion were detected, and it was shown that M-LBLF could resist the digestion in simulated oral fluid (SOF) and gastric fluid (SGF), and enhance the slow-release ability of LBLF in simulated intestinal fluid (SIF), indicating that microencapsulation can improve the stability of LBLF and play a slow-release role.

Nanocrystalline CoOxglass for highly-efficient alkaline hydrogen evolution reaction

We report that the nanocrystalline CoOxglass composed of mixed amorphous parts and crystalline domains shows high-performance for electrochemical hydrogen production because of the synergistic effects among the nanocrystals and amorphous matrix.

Physico-Chemical Characterization of Keratin from Wool and Chicken Feathers Extracted Using Refined Chemical Methods.

In this work, the characteristic structure of keratin extracted from two different kinds of industrial waste, namely sheep wool and chicken feathers, using the sulfitolysis method to allow film deposition, has been investigated. The structural and microscopic properties have been studied by means of scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), and infrared (IR) spectroscopy. Following this, small-angle X-ray scattering (SAXS) analysis for intermediate filaments has been performed. The results indicate that the assembly character of the fiber can be obtained by using the most suitable extraction method, to respond to hydration, thermal, and redox agents. The amorphous part of the fiber and medium range structure is variously affected by the competition between polar bonds (reversible hydrogen bonds) and disulfide bonds (DB), the covalent irreversible ones, and has been investigated by using fine structural methods such as Raman and SAXS, which have depicted in detail the intermediate filaments of keratin from the two different animal origins. The preservation of the secondary structure of the protein obtained does offer a potential for further application of the waste-obtained keratin in polymer films and, possibly, biocomposites.

Effects of accelerated weathering on properties of 3D-printed PLA scaffolds

This work aims to analyze the effects of accelerated weathering – under different environmental variables – on the properties of poly(lactic acid) (PLA) scaffolds fabricated by Fused Filament Fabrication (FFF). Two methodologies were followed: at 35 and 45 °C, under temperature control alone (ASTM F1980), and under controlled cycles of temperature, ultraviolet (UV) radiation, and humidity (ASTM G154). Weathered samples were characterized by color visual analysis, differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). For weathering tests at 35 °C, and simultaneous control of temperature, radiation, and humidity (T-R-H), the degradation seemed to predominantly affect amorphous parts of the PLA scaffolds. For weathering at 45 °C, the degradation was prevalent on amorphous parts for initial exposure and, subsequently, also affected crystalline parts of the polymer. The accelerated weathering tests produced changes in the FTIR spectra, indicating intensified chain scissions by photolysis and hydrolysis, with more pronounced effects for the T-R-H test, followed by the tests under 45 °C and 35 °C. Noticeable surface defects appeared only on PLA samples subjected to the T-R-H test (336 h exposure), as a result of the more severe degradation generated by the combined variables of this accelerated weathering. • Poly(lactic acid) (PLA) scaffolds manufactured by Fused Filament Fabrication (FFF) • Different accelerated weathering tests performed with the PLA scaffolds • Changes in properties, due to weathering, assessed and compared • Effects of weathering tests linked to PLA degradation mechanisms

Lodging resistance of rice plants studied from the perspective of culm mechanical properties, carbon framework, free volume, and chemical composition

In this study, four varieties of rice were cultivated on the same farmland under same conditions and for same duration. However, their lodging resistance was found to be obviously different from each other. Herein, three key factors that highly influenced the lodging resistance were identified. First, in terms of morphological trait, in contrast to the generally believed theory that the overall thickness of the fresh culm wall governs the strength, the thickness of the depressed region of the dried basal culm wall largely determined the mechanical properties by acting as the weak link. This depressed region represents the vulnerable part with high syneresis rate. Second, the culm and its carbon framework exhibited sufficient strength and rigidity for both support and stability of the rice stem. The constraint of high lodging resistance of rice plants is attributed to the culm flexibility. Furthermore, the results of the positron annihilation lifetime spectroscopy corroborate that the most amorphous part and the highest-fraction free volume in the culm carbon framework were found for samples that exhibited high lodging resistance. This result confirmed the significant influence of the culm flexibility on lodging resistance. Third, a higher level of nitrogen element content in the basal culm can benefit its growth and development, which may contribute to an increase in lodging resistance of rice plants.

Predictive simulation of bulk metallic glass crystallization during laser powder bed fusion

Laser powder bed fusion (L-PBF) has been employed to fabricate bulk metallic glass (BMG) parts. However, traditional experimental trial-and-error methods to determine process parameters for specific materials and L-PBF machines are time-consuming and expensive. In this paper, a phenomenological crystallization model, namely the Nakamura model, is coupled with L-PBF process simulation. A convenient approach for the crystallization parameter determination and a two-step Euler method for the numerical implementation has been developed. Numerical simulations are performed using the material parameters of a Zr-based BMG Zr59.3Cu28.8Al10.4Nb1.5 (at.%, trade name: AMZ4). The numerical results are validated by comparing with experimental results from different perspectives. Based on the numerical findings, a comprehensive understanding of BMG crystallization behavior during L-PBF is gained. In the end, the crystallization model is implemented in our in-house developed software SAMPLE2D. SAMPLE2D simulation results are presented, whereby the L-PBF process window for fully amorphous AMZ4 parts is explored. Thereby, it is believed that the developed numerical software can be applied to aid process development for BMGs by taking the crystallization phenomenon into account.

"COMPATIBILITY OF MODIFIED HERACLEUM SOSNOVSKYI CELLULOSE-BASED MATERIAL WITH SOME POLYMERS "

The aim of the present work was to investigate the compatibility prediction of Heracleum sosnovskyi plant material, modified with monoethanolamine (N→B)-trihydroxyborate, with organopolymer binders, such as polyvinyl acetate, polyurethane and casein. To achieve the goal, the following tasks were solved: first, the composition of the modified plant materials was studied and the degree of their antifungal resistance was determined; and then, the compatibility of the modified cellulosic material and organopolymer binders was predicted based on the calculation of the Hildebrand solubility parameter by determining the cohesive energy and the van der Waals volume of elementary bonds of the modified substrate. The investigation showed that the modification of plant raw materials results in the removal of the amorphous part of the lignin-carbohydrate complex of cell walls (lignin and hemicelluloses) from the substrate composition and chemical interaction of the modifier with secondary cellulose hydroxyls. This makes the plant material fully biostable and thus it can be used in the development of composite materials. The method of mutual solubility calculation can be used to predict the compatibility of the modified plant material with organopolymer binders. Based on this method, it was found that the best compatibility is observed when an excess of casein and polyurethane are used as binders for the modified cellulose-based material. Two formulations, namely casein (excess)-modified cellulose-based material and polyurethane (excess)-modified cellulose-based material, can be recommended for developing composites.