Different Degrees Of Crystallinity Research Articles

Dissolution of aluminum hydroxide to provide Al and to neutralize acidity for the removal and recovery of fluoride through cryolite crystallization

Dissolution of aluminum hydroxide (Al(OH)3(s)) was investigated for providing Al and at the same time neutralizing the acidity generated in the recovery of fluoride through the crystallization of cryolite. The alkalinity provided by the dissolution of Al(OH)3(s) combined with Na2CO3 reduces the total treatment cost for fluoride recovery by 45%, compared to when other aluminum salts were used. In this study, two types of aluminum hydroxide having different degrees of crystallinity of 61.53% and 25.57%, denoted as crystalline Al(OH)3(s) (CAH) and amorphous Al(OH)3(s) (AAH), respectively, were investigated. The results showed that the dissolution of AAH was very efficient but an excess amount of AAH adsorbed the freshly formed AlFx3−x complexes, impairing the purity of cryolite. On the other hand, the dissolution of the CAH was mostly dependent on the time, the Al dosage, and the initial pH of the solution. Upon reaching equilibrium, the dissolved Al to the initial F molar ratio reached 2/6. With the mixed volume ratio of 1:1 between the raw HF solution and the HF solution being equilibrated with CAH initially, the removal of F reached 96% and the cryolite formation was positively confirmed based on the XRD analysis of the resulting solid.

Cobalt Phosphide Nanoparticles Synthesized by Solvothermal Phosphidization of Metal-Organic Frameworks for Electrocatalytic Oxygen Evolution

Active and stable electrocatalysts for oxygen evolution reaction (OER) are crucial in the widespread application of water electrolyzers. Cobalt phosphide nanoparticles (Co-P) with different degrees of crystallinity are synthesized via solvothermal phosphidization of Co metal-organic frameworks and P4 using different solvents. The Co-P can be converted to active OER electrocatalysts in 1 M KOH, with the most active reaching 10 mA cm-2 OER current densities at 270 mV overpotential. The OER intermediate adsorption energy is tuned by the electron interactions in the crystalline/amorphous heterostructured Co-P, which show the highest intrinsic OER activity. After the long-term OER in base, surface phosphides are converted to (oxy)hydroxides that are the active species towards OER.

Amorphous RuCoP Ultrafine Nanoparticles Supported on Carbon as Efficient Catalysts for Hydrogenation of Adipic Acid to 1,6-Hexanediol.

As an important raw material for organic synthesis, the 1,6-hexanediol (HDOL) is synthesized by the complicated two-step process traditionally. The hydrogenation of adipic acid (AA) is a potential way to prepare 1,6-hexanediol. At present, amorphous RuMP (M: Co, Ni, Fe, etc.)-based alloys with low Ru content were developed by co-precipitation as the efficient catalysts for converting AA to HDOL via hydrogenation. Among these RuMP catalysts, RuCoP alloys exhibited the highest selectivity and yield to HDOL owing to the electronic effect. The selectivity and yield of HDOL for the optimized RuCoP/C sample was achieved to 80% and 64%, respectively, at 65 bar and 220 °C. A series of RuCoP alloys with different degrees of crystallinity and particle sizes were prepared to investigate the effect of morphology and structure on its catalytic performance. The results indicated that the high catalytic activity of RuCoP/C resulted from its rich active sites due to its amorphous phase and small particle size.

Effect of Crystallinity on Young's Modulus of Porous Materials Composed of Polyethylene Terephthalate Fibers in the Presence of Carbon Dioxide.

Carbon dioxide (CO2)-assisted polymer compression method is used for plasticizing polymers with subcritical CO2 and then crimping the polymer fibers. Given that this method is based on crimping after plasticization by CO2, it is very important to know the degree of plasticization. In this study, heat treatment was gently applied on raw material fibers to obtain fibers with different degrees of crystallinity without changing the shape of the fibers. Simultaneously, two types of sheets were placed in a pressure vessel to compare the degree of compression and the degree of hardness. Furthermore, a model was used to derive the relative Young’s modulus of porous materials composed of polymer fibers with different degrees of crystallinity. In the model, the amount of strain was calculated according to the Young’s modulus as a function of porosity and reflected in compression. Young’s modulus of porous polymers in the presence of CO2 has been shown to vary significantly with slight differences in crystallinity, indicating that extremely low crystallinity is significant for plasticizing the polymer by CO2.

Influence of structural disorder on the photocatalytic properties of ZnS nanocrystals prepared by the one-pot solvothermal approach

This study focuses on the impact of the sulfur vacancies on the photocatalytic response of the ZnS nanocrystals synthesized by solvothermal method varying the concentration of zinc acetate/thiourea precursors. XRD patterns show that these samples have a hexagonal structure with different degrees of crystallinity, varying the crystallite size from 2.48 to 2.85 nm. The UV-Vis data reveals an absorption peak (at about 320 nm) characteristic of ZnS nanocrystals. As a result, a decrease in the bandgap value of these materials was observed from 3.78 to 3.62 eV. In principle, a comparison of these results and theoretical calculations reveals the formation of intermediate levels inside the bandgap due to structural polarization. These findings also corroborate the zeta potential measured for these samples, evidenced by an increase of positive charge of ZnS surfaces. Also, the low Miller-index surfaces, such as (100), (110) and (0001), were investigated by periodic density functional theory calculations, in nice agreement with the experimental data. A photocatalysis mechanism was investigated and confirmed the formation of reactive oxygen species.

EFFECT OF CALCINATION TEMPERATURE ON THE PROPERTIES AND CATALYTIC PERFORMANCE OF NICKEL OXIDE IN THE ETHANE OXIDATIVE DEHYDROGENATION REACTION

In this paper, the catalytic behavior of nonstoichiometric nickel oxides was investigated in the ethane oxidative dehydrogenation reaction (ODH). The oxide was obtained by heat treatment in the range 250 – 400°C of β-Ni(OH)2 synthesized by precipitation-oxidation. The structural properties of the catalysts were characterized by XRD, FTIR, UV-vis, and SEM. The selective ODH reaction was quantified by gas chromatography. The samples showed pure NiO cubic structure with different degrees of crystallinity, crystallite size, and specific surface area. The increase of calcination temperature caused an increase in the average crystallite size from 28 Å at 250 °C to 104 Å at 400 °C, whereas the shape of the particles showed no significant differences; pore diameter increased from 35 Å to 69 Å and specific surface area decreased from 245 to 82 m2/g. The test carried out at 240°C showed a decrease in conversion, from 8.75% to 4.25%; the more crystalline samples displayed the highest intrinsic activity with selectivity to ethene close to 60%. No influence of band-gap energy on catalytic properties was observed.

СТРУКТУРА ТА ВЛАСТИВОСТІ МОДИФІКОВАНИХ ГЛІЦЕРИНОМ ПОЛІЛАКТИДНИХ ПЛІВОК

The structure and properties of modified poly(lactiс acid) films suitable for use as packaging materials and paper lamination were studied. Modification of poly(lactiс acid) of different degrees of crystallinity with glycerol was performed. The influence of film formation conditions, the amount of glycerin plasticizer, the nature of poly(lactiс acid) on the structure, surface morphology and physical and mechanical properties of modified poly(lactiс acid) materials was studied. Modified film materials can be recommended for use in the packaging industry and paper lamination.

Evolution of C–S–H in lime mortars with nanoparticles: Nanostructural analysis of afwillite growth mechanisms by HRTEM

AbstractThis work studies the formation of calcium–silicate–hydrates (C–S–H) in lime mortars prepared with additions of nano‐Ca(OH)2 and nano‐SiO2 at 23.3°C. Mineral identification was carried out by X‐ray diffraction after 10, 30, 90, and 120 days of curing. The nanoscale study starts from the generation of amorphous phases until the development of crystalline phases. Observations of binder mortar made by transmission electron microscopy (low magnification and high resolution TEM) after 30 and 110 days of curing showed the formation of two types of C–S–H with different degrees of crystallinity depending on the curing time. The development of short‐range order C–S–H globular phases was visible after 30 days. C–S–H evolved into lamellar crystalline phases visible after 110 days of curing. The crystalline phase corresponds to the C–S–H known as afwillite (Ca3(SiO3OH)2·2H2O), first reported to affect cement and concrete's mechanical and hydration properties. It appears as isolated fibers, growing epitaxially along the edges of the calcite (product of the carbonation of Ca(OH)2), and advancing inward aided by atomic defects (grain boundaries, stacking faults). In addition, high‐resolution transmission electron microscopy tools and electron diffraction simulation confirmed a monoclinic symmetry for afwillite crystals. These results contribute to analyzing the presence of crystalline/amorphous C–S–H in lime mortars, providing information on the structure of afwillite and its possible effects on the binder materials.

Layered Double Hydroxides (LDHs) as New Consolidants for Cultural Heritage Masonry

(1) Background: In time, stone monuments suffer a process of aging and loss of aesthetic and mechanical properties. In order to restore and stop the loss of their properties, various treatments are used, and in this context, a new class of discovered materials with interesting properties are layered double hydroxides, or LDHs. (2) Methods: The LDHs, prepared by a coprecipitation method, were characterized by the structure by X-ray diffraction, composition by FT-IR spectroscopy and X-ray fluorescence spectroscopy, size by diffuse light scattering, and porosity by N2 adsorption/desorption. Additionally, some microscopy techniques such as optical microscopy and SEM/EDAX were used for surface aspects and morphology, and finally, all these were checked with ImageJ software for representative roughness parameters of the treated surfaces by brushing or incorporation. (3) Results: The prepared materials show different degrees of crystallinity and textural properties, and the dispersion of the material presents good stability in time in water/ethanol mixtures. Treatment with the LDH dispersion applied by brushing led to improvements in the mechanical properties (about a 5% increase in compressive strength), to an increased surface stability (about 30%), and to an improvement in the resistance to freeze–thaw cycles. The textural properties of the specimens’ materials were not altered by these treatments. (4) Conclusions: The order of the consolidation efficacity was CaMgAl-LDH > MgAl-LDH > CaAl-LDH, better for application by brushing than by incorporation.

Spectra of Internal Friction in Polyethylene.

The study of spectra of internal friction and temperature dependencies of frequency of freely damped oscillatory process excited in investigated samples of polyethylene with different degree of crystallinity in the temperature range from −150 C to +150 C. It is established that four local dissipative processes of different intensity shown in different temperature intervals are observed on the spectra . These are , , , processes. The theoretical analysis of the relationship between the anomalous changes of the vibrational process frequency and the shift modulus defect and the internal friction mechanisms for each of the dissipative loss processes detected on the spectrum is carried out. The influence of supramolecular structures on local dissipative process in polyethylene is estimated.

Influence of MnO2-Birnessite Microstructure on the Electrochemical Performance of Aqueous Zinc Ion Batteries

KxMnO2 materials with birnessite-type structure are synthetized by two different methods which make it possible to obtain manganese oxides with different degrees of crystallinity. The XPS results indicate that the sample obtained at high temperature (KMn8) exhibits a lower oxidation state for manganese ions as well as a denser morphology. Both characteristics could explain the lower capacity value obtained for this electrode. In contrast, the sample obtained at low temperature (KMn4) or by hydrothermal method presents a manganese oxidation state close to 4 and a more porous morphology. Indeed, in this case higher capacity values are obtained. At current density of 30 mA g−1, the KMn8, KMn4, and HKMn samples display a capacity retention of 88, 82, and 68%, respectively. The higher capacity loss obtained for the HKMn compound could be explained considering that the incorporation of Zn2+ in the structure gives rise to the stabilization of a ZnMn2O4 spinel-type phase. This compound is obtained in the discharge process but remains in the charge stage. Thus, when this spinel-type phase is obtained the capacity loss increases. Moreover, the stabilization of this phase is more favorable at low current rates where 100% of retention for all samples, before 50 cycles, was observed.

Novel spherical lactose produced by solid state crystallisation as a carrier for aerosolised salbutamol sulphate, beclomethasone dipropionate and fluticasone propionate

The purpose of the present work was to engineer lactose carrier particles for inhalation using a solid-state crystallisation of amorphous spray dried lactose approach. A suspension of spray dried lactose was contacted with hot ethanol for 10 and 30 s to produce spherical particles (ESDL10) and (ESDL30) with different degrees of crystallinity, particle size, and controlled surface rugosity. Lactohale® (control) and engineered spray dried lactose (ESDL) particles were characterised by Scanning Electron Microscopy, X-ray Powder Diffraction and Tribo-electrification. Lactohale® and engineered lactose particles were mixed separately with salbutamol sulphate (SS), beclomethasone dipropionate (BDP) and fluticasone propionate (FP) and each formulation was assessed for drug content uniformity, drug segregation after tribo-electrification and drug deposition using Andersen Cascade Impactor (ACI). Lactohale® showed the highest but opposite affinity for electrical surface charges compared to engineered lactose. Lactohale® showed the greatest variation in drug content uniformity with SS but to a lesser extent with BDP and FP, whereas the ESDL carriers produced an acceptable uniform mix with all drugs. SS-Lactohale® formulation showed the highest segregation after tribo-electrification up to 119-fold in comparison to that observed with SS-engineered lactose. ESDL10 carrier promoted a better drug deposition for both BDP and FP and showed the least variation in both content uniformity and FPD with all three drugs. Therefore, production of crystalline spherical lactose carrier with controlled surface texture, size and crystallinity is achievable using solid state crystallisation for DPIs, whilst providing less variation in drug content uniformity and consistent fine particle dose to the lungs in-vitro for both hydrophilic and hydrophobic drugs.

Color Stability, Chemico-Physical and Optical Features of the Most Common PETG and PU Based Orthodontic Aligners for Clear Aligner Therapy.

It is difficult to find research papers collecting comparative results about characterization studies of clear aligners. Therefore, the aim of this paper is to provide the first comparative analysis of most commercial clear aligners, in terms of their stability towards intra-oral staining agents, their physicochemical and optical properties, as well as their water absorption behavior. Five types of aligners, characterized by different techniques, are considered: Erkodur, Essix Plastic, Ghost Aligner, Zendura, and Invisalign. The obtained results show that clear aligners are made up of PETG, semi rigid PU, and a mixture of PU and PETG, with different degrees of crystallinity which affect the transparency of each aligner. In particular, the PETG-based materials reveal the highest value of short-range order and the highest properties in terms of transparency in the visible range. After 14 days of immersion into red wine and coffee, PETG and PU-based aligners reveal a perceivable change in color (NBS values from 1.5 to 3), corresponding to a loss of transparency due to the deposition of impurities on the surface. These results are particularly marked for Invisalign, showing changes towards other colors (NBS up to 35), probably due to the thermoforming process which led to the formation of a wrinkled surface entrapping the impurities.

Crazing and Toughness in Diblock Copolymer-Modified Semicrystalline Poly(l-lactide)

Sustainable semicrystalline poly(l-lactide) (PLLA) was melt mixed with 5 wt % poly(ethylene oxide)-b-poly(butylene oxide) (PEO-PBO) diblock copolymer, resulting in blends that display an exceptional combination of properties. The blends were annealed at various temperatures, leading to different degrees of crystallinity. The addition of 5 wt % PEO-PBO produced finely dispersed liquid particles that caused a significant reduction in the time for crystallization after quenching from the melt, where Tm = 166 °C. At 95 °C, the halftime for crystallization was t1/2(95 °C) = t1/2o/7, while at 135 °C, t1/2(135 °C) = t1/2o/5, where t1/2o is the time required to obtain 50% of the final extent of crystallization with pure PLLA. The block copolymer particles also enhanced the ductility of the blends by facilitating stress-induced cavitation and uniform crazing without impacting the modulus. Tensile toughness increased by 7–15 fold, scaling inversely with the degree of crystallinity. The deformation mechanism was investigated by small- and wide-angle X-ray scattering as a function of applied strain, revealing that the craze volume is dependent on crystallinity, while the crystal structure displayed minimal changes. Regardless of the extent of crystallinity, crazing was found to be the primary deformation mechanism, countering the ductile-to-brittle transition associated with the aging of PLLA. Adding 5 wt % PEO-PBO extends the strain at break from 4% for pure PLLA after 2 days to more than approximately 50% after 85 or more days of aging. These findings, along with the industrially relevant blend preparation method, reveal that PEO-PBO is a unique and potent additive that could expand the applications served by PLLA, promoting a more sustainable future.

Understanding Solid Electrolyte Interphase Nucleation and Growth on Lithium Metal Surfaces

Experiments and theory are needed to decode the exact structure and distribution of components of a passivation layer formed at the anode surface of Li metal batteries, known as the Solid Electrolyte Interphase (SEI). Due to the inherent dynamic behavior as well as the lithium reactivity, the SEI structure and its growth mechanisms are still unclear. This study uses molecular simulation and computational chemistry tools to investigate the initial nucleation and growth dynamics of LiOH and Li2O that provide us with thermodynamics and structural information about the nucleating clusters of each species. Following the most favorable pathways for the addition of each of the components to a given nascent SEI cluster reveals their preferential nucleation mechanisms and illustrates different degrees of crystallinity and electron density distribution that are useful to understand ionic transport through SEI blocks.

Application of CO2-Assisted Polymer Compression to Polylactic Acid and the Relationship between Crystallinity and Plasticization

CO2-assisted polymer compression (CAPC) is an environmentally friendly processing method that uses CO2 to plasticize and crimp polymer fibers at room temperature, enabling low-energy processing within a short time. In this study, CAPC was applied to polylactic acid (PLA), a carbon-neutral polymer. To evaluate the relationships between CO2 plasticization and the crystallinity degree and plasticization of PLA, samples with different degrees of crystallinity were layered and simultaneously compressed to observe the most collapsed layer. The sample with lower crystallinity exhibited better crushing and higher plasticization than the crystallized samples. The PLA with high crystallinity developed cracks on the fiber surfaces with consequent loss of strength. Based on the results, CAPC is a potentially effective method for PLA with low crystallinity.

ДОСЛІДЖЕННЯ ФІЗИЧНОЇ МОДИФІКАЦІЇ ПОЛІЛАКТИДІВ

The physical modification of poly(lactiс acid) materials suitable for use in the form of films for the packaging industry and paper lamination has been studied. Modification of poly(lactiс acids) of different degrees of crystallinity with glycerol was performed. The peculiarities of the formation of film materials on the basis of poly(lactiс acids) and their mixtures with glycerin are investigated, the choice of the optimal solvent (chloroform) for the formation of films by irrigation is substantiated and carried out. Concentration and temperature-time characteristics of formation of modified poly(lactiс acid) films are determined. On the basis of the performed researches the main stages of manufacturing of modified poly(lactiс acid) films are substantiated and their physical and mechanical properties are investigated.

Nucleation and Growth of Solid Electrolyte Interphase on Lithium Metal Batteries

Lithium metal anode is considered a great candidate because of its high theoretical capacity and negative electrochemical potential. However, key factors like poor cyclability as well as the safety issues related to the uneven lithium electrodeposition, dendrite growth, and unstable solid electrolyte interphase (SEI) are keeping lithium metal batteries away from commercialization. Different attempts both experimentally and theoretically have been done to decode the exact structure and distribution of SEI, but due to the inherent dynamic behavior as well as the lithium reactivity, the exact structure of the SEI and its growth mechanisms are still unclear. In this study with the use of molecular simulation and computational chemistry tools, we investigate the initial nucleation and growth dynamics of different SEI components that provide us with thermodynamics and structural information about the nucleating SEI.Different nucleation and growth mechanisms were studied for the SEI components including LiF, Li2O, and LiOH. An initial mechanism of nucleation is based on the assumption that a Li metal cluster represents a portion of the surface where inhomogeneous Li seeds are nucleating, we use ab initio methods to determine the preferential addition sites for OH or O radicals or fluorine anions. This mechanism allows the study of different structures of SEI in lithium-rich environments simulating initial stages of electrolyte decomposition and SEI formation. Multiple models are studied to understand the formation energies and structures for SEI nanocluster formation in which already formed fragments of SEI are joined together to study the formation of larger SEI clusters. Each of the different components of SEI reveals its preferential growth mechanisms showcasing different degrees of crystallinity and electron density distribution leading to a better understanding of the nucleation and growth of SEI.

NiCo-layered double hydroxide/g-C3N4 heterostructures with enhanced adsorption capacity and photoreduction of Cr(VI)

Photo-catalytic reduction of highly toxic Cr(VI) using graphitic carbon nitride (g-C3N4) based photocatalysts under visible light irradiation condition has been attracting considerable attention recent years. Here, we report the development of heterostructured NiCo-layered double hydroxides (LDHs) grown horizontally on g-C3N4 nanosheets with different degrees of crystallinity (amorphous to crystalline), NiCoLDH/g-C3N4, with high photocatalytic activity for the reduction of toxic hexavalent chromium ions (Cr(VI)) as well as high adsorption capability for congo red (CR) photodegradation under visible light irradiation. The presence of NiCoLDH nanoparticles promotes the adsorption of the anionic pollutants while g-C3N4 in the heterostructure promotes fast photodegradation of CR and reduction of Cr(VI). The NiCoLDH/g-C3N4 composite prepared using amorphous-crystalline g-C3N4 homojunctions shows the best adsorption performance. The kinetic data demonstrates improved correlation coefficient for the pseudo-second-order (R2 > 0.99) and Freundlich isotherm model. The NiCoLDH/g-C3N4 composite shows an improved separation efficiency of photogenerated electron and hole pairs, leading to its improved Cr(VI) adsorption and photo-reduction performance. The monolayer adsorption capacities of CR and Cr(VI) of the NiCoLDH/g-C3N4 heterostructured composite can be as high as 1100 and 46 mg/g at 30 °C, respectively. This work provides new perspectives for the development of highly efficient g-C3N4-based composite photocatalysts for wastewater treatment related applications.

Dry tribological performance of nanostructured 2D turbostratic graphite particles derived from boron and chromium carbides

Nanostructured turbostratic graphite derived from the solid-state dissociation of carbides is a new kind of carbide-derived carbon (CDC) consisting of heavily misaligned graphene layers. A recently developed processing route was used to obtain 2D turbostratic graphite nanoparticles via solid-state reactions between boron and chromium carbides. In this work, the tribological performance of these new CDC nanoparticles with different degrees of crystallinity was evaluated. Vacuum impregnation of a tailored sintered porous matrix (Astalloy CrL + 0.6%C) was used to obtain self-lubricating specimens containing both CDC and commercial crystalline 3D graphite, used as a reference. The results showed that the CDC particles promoted low friction coefficients (~0.1) and wear rates up to 70% lower than that of commercial crystalline graphite particles. The study of the wear scars through SEM and an extensive Raman spectroscopy analysis indicated that, although carbon crystallinity plays a fundamental role in the tribological behaviour, it is not the only variable to be considered, as the slow release of solid lubricant from the pores during the tests was shown to be crucial for the stability of a lubricious tribolayer, which reduces adhesion and wear.