Crystalline Modifications Research Articles

The proposed mechanism of glow of mesosphere clouds

The question of the physical mechanism of electromagnetic radiation scattering by mesospheric (noctilucent) clouds is considered. A hypothesis has been expressed about the special electromagnetic characteristics of nanometer-sized ice particles that make up mesospheric clouds. Particle ice consists of a recently discovered crystalline modification of water — ice 0, formed by the condensation of vapor on dust particles at temperatures of –140…–23°C. Ice 0 is a ferroelectric, and upon contact with a dielectric, a layer with high electrical conductivity is formed. Due to plasmon resonance in nanosized layers, strong scattering of electromagnetic radiation occurs over a wide frequency range. This mechanism causes the glow of noctilucent clouds when illuminated by the radiation of the Sun.

Effect of powder morphology on the structure and properties of Al2O3 based coatings obtained by detonation spraying

Aluminum oxide (Al2O3) remains a crucial material in the field of engineering ceramics, particularly in industrial applications. Notably, its transitional phases, in addition to the α-phase, demonstrate good properties. In this article the structure and properties of coatings obtained by detonation spraying from aluminum oxide powder with different production methods (fragmentation and spherical particle shape) and crystalline modification (α-Al2O3 and γ-Al2O3) but with similar average particle size were studied. The goal of the study was to investigate the influence of the morphology and phase composition of the powder on such properties of the coatings as microstructure, porosity, roughness and hardness. The results of the study showed that agglomerated spherical powder leads to low porosity of the coatings, while crushed fragmentation particles provide dense layers. In addition, the coating obtained using fragmentation powder showed higher hardness, and the surface had twice the roughness, compared to the coating applied using spheroidal powder. These results confirm the effect of the morphology of the original powder on the final properties and efficiency of the coatings. The study showed that the detonation spraying method allows for the efficient application of coatings from two types of Al2O3 powders with different morphology (spherical and fragmentation) and phase composition (γ-Al2O3and α-Al2O3) but with similar particle sizes.

Modification of the Surface Crystallinity of Polyphenylene Sulfide and Polyphthalamide Treated by a Pulsed-Arc Atmospheric Pressure Plasma Jet.

Atmospheric plasma jets generated from air or nitrogen using commercial sources with relatively high energy densities are commonly used for industrial applications related to surface treatments, especially to increase the wettability of polymers or to deposit thin films. The heat fluxes to which the substrates are subjected are typically in the order of 100-300 W/cm2, depending on the treatment conditions. The temperature rise in the treated polymer substrates can have critical consequences, such as a change in the surface crystallinity or even the surface degradation of the materials. In this work, we report the phase transitions of two semicrystalline industrial-grade polymer resins reinforced with glass fibers, namely polyphenylene sulfide (PPS) and polyphthalamide (PPA), subjected to plasma treatments, as well as the modeling of the associated heat transfer phenomena using COMSOL Multiphysics. Depending on the treatment time, the surface of PPS becomes more amorphous, while PPA becomes more crystalline. These results show that the thermal history of the materials must be considered when implementing surface engineering by this type of plasma discharge.

SPHERICAL AGGLOMERATION OF TELMISARTAN - AN APPROACH TO IMPROVE PHYSICOCHEMICAL PROPERTIES

The study explains the preparation of spherical agglomerates (SA) of telmisartan (TLS), a BCS class II drug used to improve it’s physicochemical and bulk properties. Drugs of this class could potentially exhibit dissolution rate limited absorption. TLS spherical agglomerates were designed using hydrophilic polymer (PVP K-30), dimethyl formamide (DMF), water and ethyl acetate (bridging liquid) by solvent change method and evaluated for micromeritic properties. The SA were characterized by particle size determination, FTIR, PXRD and SEM. The results of micromeritic studies indicated that SA showed improved flow properties due to their spherical shape and bigger size. Absence of strong interaction at molecular level and alteration in the crystal structure of TLS with modification in crystallinity was confirmed by FTIR and PXRD respectively. TLS solubility characteristics were improved by this approach.

Dodecyl Surfactants Induced Crystalline Modifications in Polyamide-6 Nanofibers

Dodecyl Surfactants Induced Crystalline Modifications in Polyamide-6 Nanofibers

Synthesis of Technetium Carboxylates: Wheel-Like Octanuclear Clusters (Tc8(μ-O)8(RCOO)16, Where R = CF3, C6H5)─Potential Nanobuilding Units for Tc-MOFs.

Herein, we studied the behavior of TcO4- in trifluoroacetic anhydride (TFAA) under visible light irradiation in situ by UV-vis spectroscopy. One carboxylate of Tc(VII) C2F3O5Tc (1) and two wheel-like carboxylate clusters of Tc(IV) Tc8(μ-O)8(CF3COO)16 (2, 3) and Tc8(μ-O)8(C6H5COO)16 (4) were synthesized and analyzed using pXRD, TGA, UV-vis spectroscopy, and SCXRD techniques. According to SCXRD, it was found that Tc(IV) trifluoroacetate exists in two crystalline modifications. By UV-vis spectroscopy and DFT calculations, it was shown that the primary compound in the reaction system is trifluoroacetate Tc(VII). A technetium trifluoroacetate(VII) and Tc intermediates of unidentified nature both show photosensitivity. The influence of intermolecular noncovalent interactions on the volatility of trifluoroacetate and benzoate Tc(IV) is shown. The main regularities of chemical transformations of technetium in nonaqueous solutions of carboxylates have been revealed. The obtained data on the kinetics of the process suggest that technetium in trifluoroacetic anhydride can simultaneously exist in the form of Tc(VII), Tc(VI), Tc(V), and Tc(IV). Under laser ionization or prolonged heating, the formation of the Tc(II,III)-cluster is observed.

Alpha nickel hydroxide electrodes improve aqueous rechargeable batteries capacity

Nickel hydroxide electrode materials have been improved for the use in Ni-based rechargeable batteries such as Ni-H2, NiMH, NiCd, NiFe, and NiZn batteries. A stabilized α-phase Ni1-xAlx(OH)2, synthesized using wet chemical coprecipitation methods while controlling pH accurately followed by hydrothermal treatments at 165 °C, is reported. Variations in synthetic routes, dopants and morphology had strong influence on the electrochemical performance. Morphological control, crystallinity and surface modification by Co(OH)2 were important for the better performance. Conventional battery grade β-Ni(OH)2 is usually made of a spherical particles, but we find that circular shaped particles can be advantageous. Hydrothermal treatments increase sample crystallinity and discharge capacity. A hydrothermal treated Ni0.8Al0.2(OH)2-LDH sample reaches a discharge capacity of 368 mAh g−1 and a corresponding Ni0.9Al0.1(OH)2 reaches 405 mAh g−1. Both have a circular-like morphology and the later shows a tap density of 1.52 g cm−3 and volumetric energy density of 531 mAh cm−3. Only a modest Co(OH)2 surface coating is needed to reduce the polarization behavior, increase the redox reaction reversibility and electrode kinetics via formation of CoOOH species after electrochemical oxidation.

Bessel beam fabrication of graphitic micro electrodes in diamond using laser bursts

We present the fabrication of conductive graphitic microelectrodes in diamond by using pulsed Bessel beams in the burst mode laser writing regime. The graphitic wires are created in the bulk of a 500 μm thick monocrystalline HPHT diamond (with (100) orientation) perpendicular to the sample surface, without beam scanning or sample translation. In particular, the role of different burst features in the resistivity of such electrodes is investigated for two very different sub-pulse durations namely 200 fs and 10 ps, together with the role of thermal annealing. Micro-Raman spectroscopy is implemented to investigate the laser-induced crystalline modification, and the results obtained by using two different laser repetition rates, namely 20 Hz and 200 kHz, are compared. A comparison of the micro-Raman spectra and of the resistivity of the electrodes fabricated respectively with 10 ps single pulses and with bursts (of sub-pulses) of similar total duration has also been made, and we show that the burst mode writing regime allows to fabricate more conductive micro electrodes, thanks to the heat accumulation process leading to stronger graphitization. Moreover, the microfabrication of diamond by means of the longest available bursts (~ 46.7 ps duration) featured by 32 sub-pulses of 200 fs duration, with intra-burst time delay of 1.5 ps (sub-THz bursts), leads to graphitic wires with the lowest resistivity values obtained in this work, especially at low repetition rate such as 20 Hz. Indeed, micro electrodes with resistivity on the order of 0.01 Ω cm can be fabricated by Bessel beams in the burst mode regime even when the bursts are constituted by femtosecond laser sub-pulses, in contrast with the results of the standard writing regime with single fs pulses typically leading to less conductive micro electrodes.

Self‐nucleation in poly(butylene adipate‐co‐terephthalate) of initially different crystal forms

AbstractPoly(butylene adipate‐co‐terephthalate) (PBAT) is an important biodegradable copolymer, but its crystallization rate is slow. Herein, the effect of self‐nucleation on the crystallization behavior of PBAT with initially different crystalline modifications (melt‐crystallized specimens and as‐received pellets) was investigated. The melt‐crystallized and as‐received PBAT specimens are confirmed as the α‐ and β‐form, respectively. It is found that the self‐nucleation domains of β‐form PBAT are almost the same as those of α‐form one. After self‐nucleation, the maximum shift of the crystallization peak toward higher temperature is around 60 °C upon the followed cooling process, suggesting that self‐nucleation remarkably promotes PBAT crystallization. The self‐nucleation temperature span of self‐nucleation domain is about 10 °C, which provides substantial benefits to industrial processing. Moreover, for both the initial α‐ and β‐form PBAT, the final crystal is α‐form after self‐nucleation treatment. This work demonstrates that self‐nucleation is highly effective in enhancing PBAT crystallization.

Raisins in a Hydrogen Pie: Ultrastable Cesium and Rubidium Polyhydrides

AbstractA new method for synthesis of metal polyhydrides via high‐pressure thermal decomposition of corresponding amidoboranes in diamond anvil cells is proposed. Within this approach, molecular semiconducting cesium (P4/nmm‐CsH7, P1‐CsH15+x) and rubidium (RbH9‐x) polyhydrides with a very high hydrogen content reaching 93 at.% are synthesized. Preservation of CsH7 at near ambient conditions, confirmed both experimentally and theoretically, represents a significant advance in the stabilization of hydrogen‐rich compounds. In addition, two crystalline modifications of RbH9‐x with pseudohexagonal and pseudotetragonal structures identified by synchrotron X‐ray diffraction, and Raman measurements are synthesized. Both phases are stable at 8–10 GPa. This is an unprecedentedly low stabilization pressure for polyhydrides. These discoveries open up possibilities for modifying existing hydrogen storage materials to increase their efficiency.

Synthesis, crystal structure and Hirshfeld analysis of N-ethyl-2-{3-methyl-2-[(2Z)-pent-2-en-1-yl]cyclo-pent-2-en-1-yl-idene}hydrazinecarbo-thio-amide.

The title compound (C14H23N3S, common name: cis-jasmone 4-ethyl-thio-semicarbazone) was synthesized by the equimolar reaction of cis-jasmone and 4-ethyl-thio-semicarbazide in ethanol facilitated by acid catalysis. There is one crystallographically independent mol-ecule in the asymmetric unit, which shows disorder of the terminal ethyl group of the jasmone carbon chain [site-occupancy ratio = 0.911 (5):0.089 (5)]. The thio-semicarbazone entity [N-N-C(=S)-N] is approximately planar, with the maximum deviation of the mean plane through the N/N/C/S/N atoms being 0.0331 (8) Å, while the maximum deviation of the mean plane through the five-membered ring of the jasmone fragment amounts to -0.0337 (8) Å. The dihedral angle between the two planes is 4.98 (7)°. The mol-ecule is not planar due to this structural feature and the sp 3-hybridized atoms of the jasmone carbon chain. Additionally, one H⋯N intra-molecular inter-action is observed, with graph-set motif S(5). In the crystal, the mol-ecules are connected through pairs of H⋯S inter-actions with R 2 2(8) and R 2 1(7) graph-set motifs into centrosymmetric dimers. The dimers are further connected by H⋯N inter-actions with graph-set motif R 2 2(12), which are related by an inversion centre, forming a mono-periodic hydrogen-bonded ribbon parallel to the b-axis. The crystal structure and the supra-molecular assembly of the title compound are compared with four known cis-jasmone thio-semicarbazone derivatives (two crystalline modifications of the non-substituted form, the 4-methyl and the 4-phenyl derivatives). A Hirshfeld surface analysis indicates that the major contributions for the crystal cohesion are from H⋯H (70.7%), H⋯S/S⋯H (13.5%), H⋯C/C⋯H (8.8%), and H⋯N/N⋯H (6.6%) inter-faces (only the disordered atoms with the highest s.o.f. were considered for the evaluation).

Performance and Surface Modification of Cast Iron Corrosion Products by a Green Rust Converter (Mimosa tenuiflora Extract)

One of the alternative materials used for conducting conservation treatment of iron artifacts is the rust converter, since it generates barrier properties and more stable oxides. The protective properties and surface modifications from using Mimosa tenuiflora extract as a green rust converter on a gray iron oxide layer were studied. The surface characterization was carried out using a Scanning Electron Microscope coupled to an energy-dispersive X-ray spectrometer (SEM-EDS), along with infrared spectroscopy (IR), Raman spectroscopy, X-ray Diffraction (XRD), and Water Contact Angle (WCA). Electrochemical characterization was performed with an Electrochemical Impedance Spectroscope (EIS) using 3.5 wt.% NaCl as the electrolyte. According to the results of the Raman spectroscopy and XRD, the layer of corrosion products formed after 90 days in the atmosphere was composed of goethite, lepidocrocite, maghemite, hematite, and magnetite. The surface of the corrosion products was transformed with the rust converter into an amorphous and microcracked layer. By IR, the Fe-O and C-O-Fe bonds associated with the iron chelate were found with absorption bands at 1540 and 1567 cm−1, respectively. By XRD, a modification of the magnetite crystallinity was observed. Finally, the Water Contact Angle and the protective capacity of the corrosion products were improved by the presence of the rust converter.

Multi-shot near-infrared femtosecond laser tuning of silicon microring resonators

We studied multi-shot femtosecond laser surface modification as a permanent tuning technique for obtaining the desired resonance wavelengths for silicon microring resonators. In this multi-shot tuning approach, each microring resonator was irradiated with 10 or 100 laser pulses in the same location of the waveguide with selected laser fluence. The laser beam has 800 nm wavelength, 130 fs pulse duration, a Gaussian spatial profile with a beam waist radius of 13.1μm, and pulse energies of 12 nJ to 186 nJ to generate the applied range of laser fluences. The silicon microring resonators used in the study have a 15μm diameter and are coupled to a waveguide of 500 nm in width with a gap of 260 nm. We found that the multi-shot tuning curves (resonance wavelength shifts as a function of laser fluences) do not monotonically increase with laser fluences: they first increase, then plateau, and finally decrease. We observed that the laser energies required for the multi-shot case to obtain the onset of crystalline modifications and ablation are several times below the single-shot case because of the incubation effect. With proper control we can achieve both positive and negative resonance wavelength shifts with acceptable induced roundtrip waveguide losses.

Effect of temperature and time on the synthesis of calcium phosphate obtained by microwave hydrothermal method

Bioceramics are materials used in biomedical devices for bone replacement, and calcium phosphate derivatives are widely used in cases of bone defect repair. The aim was to evaluate the influence of temperature and time on the synthesis of calcium phosphate obtained by the microwave hydrothermal method on its structural and morphological characteristics with a view to application as a bone graft. The calcium phosphate powders (calcium octophosphate, hydroxyapatite and calcium triphosphate) were produced using the microwave hydrothermal method. To obtain the calcium phosphate powders, aqueous solutions of Ca (OH)2 and H3 PO4 were used and subjected to the microwave hydrothermal method at temperatures of 110°C and 130°C for 30 and 60 minutes, then calcined at 700°C for 1 hour and characterized using XRD, FTIR, SEM, particle size distribution, apparent density, and apparent porosity. The results obtained by the techniques confirm crystalline and morphological modifications, and homogeneous distribution of the particles, and the phases of interest, octophosphate, hydroxyapatite and calcium β-triphosphate, were identified. The formation of the β-TCP phase was predominant in the samples in which the microwave hydrothermal synthesis was carried out over a longer time and at a higher temperature. It was found that the proposed synthesis method was effective in terms of time/temperature, offering advantages over conventional techniques, such as improving the primary characteristics for choosing a biomaterial to be used in cases of bone regeneration.

The Hexacoordinate Si Complex SiCl4(4-Azidopyridine)2—Crystallographic Characterization of Two Conformers and Probing the Influence of SiCl4-Complexation on a Click Reaction with Phenylacetylene

4-Azidopyridine (1) and SiCl4 react with the formation of the hexacoordinate silicon complex SiCl4(4-azidopyridine)2 (2). Upon dissolving in warm chloroform, the complex dissociates into the constituents 1 and SiCl4 and forms back upon cooling. Depending on the cooling, two different crystalline modifications of 2 were obtained, which feature two different trans-conformers. Slow cooling to room temperature afforded conformer 2′, which features coplanar pyridine rings. Rapid cooling to −39 °C afforded crystals of conformer 2″, in which the planes of the pyridine ligands are nearly orthogonal to one another. Whereas 2′ resembles the molecular arrangement of various other known SiX4(pyridine)2 (X = halide) complexes, 2″ represents the first crystallographically confirmed example of a SiX4(pyridine)2 complex in this conformation. Conformers 2′ and 2″ were studied with 13C and 29Si solid state NMR spectroscopy. Their differences in 29Si chemical shift anisotropy, as well as energetic differences, were further investigated with computational analyses. In spite of the similar stabilities of the two conformers as isolated molecules, the crystal packing of 2″ is less stable, and its crystallization is interpreted as a kinetically controlled effect of seed formation. (3+2)-cycloaddition of 1 and phenylacetylene in toluene at 110 °C yields a mixture of 1-(4-pyridyl)-4-phenyl-1,2,3-triazole (1,4-3) and 1-(4-pyridyl)-5-phenyl-1,2,3-triazole (1,5-3) in approximate 1:2 molar ratio. The crystal structures of the two isomers were determined via X-ray diffraction. In chloroform (at 60 °C), this reaction is slow (less than 2% conversion within 4 h), but the presence of SiCl4 enhanced the rate of the reaction slightly, and it shifted the triazole isomer ratio to ca. 1:6 in favor of 1,5-3.

A second crystalline modification of 2-{3-methyl-2-[(2Z)-pent-2-en-1-yl]cyclo-pent-2-en-1-yl-idene}hydrazinecarbo-thio-amide.

A second crystalline modification of the title compound, C12H19N3S [common name: cis-jasmone thio-semicarbazone] was crystallized from tetra-hydro-furane at room temperature. There is one crystallographic independent mol-ecule in the asymmetric unit, showing disorder in the cis-jasmone chain [site-occupancy ratio = 0.590 (14):0.410 (14)]. The thio-semicarbazone entity is approximately planar, with the maximum deviation from the mean plane through the N/N/C/S/N atoms being 0.0463 (14) Å [r.m.s.d. = 0.0324 Å], while for the five-membered ring of the jasmone fragment, the maximum deviation from the mean plane through the carbon atoms amounts to 0.0465 (15) Å [r.m.s.d. = 0.0338 Å]. The mol-ecule is not planar due to the dihedral angle between these two fragments, which is 8.93 (1)°, and due to the sp 3-hybridized carbon atoms in the jasmone fragment chain. In the crystal, the mol-ecules are connected by N-H⋯S and C-H⋯S inter-actions, with graph-set motifs R 2 2(8) and R 2 1(7), building mono-periodic hydrogen-bonded ribbons along [010]. A Hirshfeld surface analysis indicates that the major contributions for the crystal cohesion are H⋯H (67.8%), H⋯S/S⋯H (15.0%), H⋯C/C⋯H (8.5%) and H⋯N/N⋯H (5.6%) [only non-disordered atoms and those with the highest s.o.f. were considered]. This work reports the second crystalline modification of the cis-jasmone thio-semicarbazone structure, the first one being published recently [Orsoni et al. (2020 ▸). Int. J. Mol. Sci. 21, 8681-8697] with the crystals obtained in ethanol at 273 K.

Evaluation of microscale crystallinity modification induced by laser writing on Mn3O4 thin films

Defining microstructures and managing local crystallinity allow the implementation of several functionalities in thin film technology. The use of ultrashort Bessel beams for bulk crystallinity modification has garnered considerable attention as a versatile technique for semiconductor materials, dielectrics, or metal oxide substrates. The aim of this work is the quantitative evaluation of the crystalline changes induced by ultrafast laser micromachining on manganese oxide thin films using micro-Raman spectroscopy. Pulsed Bessel beams featured by a 1 μm-sized central core are used to define structures with high spatial precision. The dispersion relation of Mn3O4 optical phonons is determined by considering the conjunction between X-ray diffraction characterization and the phonon localization model. The asymmetries in Raman spectra indicate phonon localization and enable a quantitative tool to determine the crystallite size at micrometer resolution. The results indicate that laser-writing is effective in modifying the low-crystallinity films locally, increasing crystallite sizes from ∼8 nm up to 12 nm, and thus highlighting an interesting approach to evaluate laser-induced structural modifications on metal oxide thin films.

Weather Resistance of Organosilicate Coatings in a Tropical Climate Depending on the Choice of the Pigment

The results of a study of the weather resistance of protective and decorative organosilicate coatings prepared using organosilicate compositions based on polydimethylphenylsiloxane as a binder and hydrosilicates as fillers are presented. The color of the coatings varies due to the use of pigments: natural FeOx minerals of yellow, red-brown, and brown shades of flowers. Using X-ray phase and X-ray fluorescence (XRF) analysis, it is established that the composition of minerals is primarily determined by iron oxides in the crystalline modification of hematite (α-Fe2O3) and goethite (α-FeO(OH)). Pigments contain a small number of impurity compounds of a number of elements that contribute to the color range of the coatings. Organosilicate coatings are exposed for 11 months in the tropical climate of two climatic zones of Vietnam (in the suburbs of Nha Trang and Ho Chi Minh City). The high corrosion resistance and color stability of the coatings are established during the entire test period. According to slight changes in the color and gloss, revealed by spectrophotometric and photoelectric methods, it is shown that higher resistance to solar radiation and other adverse climatic factors is typical for coatings with a brown pigment based on hematite; and the lowest, with a yellow pigment based on goethite.

Electronic structure of germanium dioxide with rutile structure according to ab initio computer simulation data

The article focuses on the electronic structure of the tetragonal crystalline modification of germanium dioxide. The electronic structure was theoretically studied by means of the full-potential linearized augmented plane wave method using the Wien2k software. Total and partial densities of electronic states were calculated. The spectra of the X-ray absorption near edge structure were simulated for various absorption edges of germanium and oxygen atoms. The Z+1 approximation method was used to calculate Ge K-, Ge L3- and O K absorption edges for the tetragonal modification of GeO2. The result obtained for the Ge K absorption edge is in good agreement with the experimental data. The Ge L3 spectrum was calculated for the first time, and the result is of predictive nature. In order to obtain a better agreement with the experimental calculations of the oxygen K absorption edge, besides the Z+1 approximation method, we also used the core hole method, including the simulation of a partial core hole. The study demonstrated that the use of a core hole with an electron charge of 0.7 results in a better agreement between the calculations and the experiment

Impact of varying Li+ concentration on the upconversion emission and temperature sensing characteristics of YVO4: Tm3+/Yb3+ phosphor

A series of Li+ codoped YVO4: Tm3+/Yb3+ phosphors were prepared by Pechini sol–gel reaction technique. Structural study of the material confirms the crystal structure of the prepared samples and also gives information about the crystallite size and phase purity with the variation of Li+ ion concentrations. Emission peaks around ∼ 476, and ∼ 799 nm corresponds to the 1G4→3H6, and 3H4→3H6 transitions, which could be seen under irradiation of NIR (980 nm) laser light. Li+ (10 mol%) codoped sample shows maximum upconversion. Li+ doping significantly increases the up-conversion emission intensities by more than 5 times for emission peaks around 476 nm and 799 nm.The possible explanation for the increase in UC (Upconversion) emission intensity is attributed to both improved crystallinity and crystal field modification around Tm3+ ions. The variation of UC emission spectra with respect to pump power was observed to investigate the underlying UC luminescent mechanism in YVO4: Tm3+/Yb3+ codoped with Li+ (10 mol%). The multiphoton involvement is observed in the power-dependent study of upconverted blue and NIR emission bands. Widely used fluorescence intensity ratio (FIR) technique was used to evaluate the temperature sensing capability of the optimized Li+ codoped phosphor. The FIR study of Stark components 3F2, and 3H4 levels indicates that this material is an efficient material for temperature sensing. The optimized sample, doped with Li+, exhibits relative sensitivity of 0.78% K−1 at a temperature of 548 K. This material have utility in both light-emitting diodes and as a temperature-sensing probe.