Stable Α-phase Research Articles

Low-Calcination Temperature to Synthesize A-Alumina From Aluminium Waste Can Using Sol-Gel Method

Many countries around the world are facing issues in managing solid waste materials; most of these wastes such as aluminium can are deposited to the landfills, leading to environmental pollution. Recycling is considered as an effective technique to manage the aluminium can waste since it can provide benefits in terms of energy savings, reduce volumes of waste and cost-effectiveness. In this article, it was desired to turn the aluminium can waste into α-Alumina using sol-gel method. Alumina exists in many crystalline structures which degenerate to the most stable hexagonal α-phase at high temperatures. α-Alumina (a-Al2O3) is the most stable crystalline structure widely used and studied as electronic packaging, corrosion resistance ceramics, high-temperature structural material, and translucent ceramics. FTIR, XRD, SEM-EDX, TGA, and BET were employed to investigate the properties of a-alumina. The experimental results obtained from this study demonstrates the possibility of producing alumina from an aluminium can waste with the exact surface area of 5.2105 m2/g, crystallite size at 132.50 nm and total weight loss of 2.71% at 900 °C calcination temperature.

Highly stable and efficient α-phase FA-based perovskite solar cells prepared in ambient air by strategically enhancing the interaction between ions in crystal lattices

An α-phase FA-based perovskite is successful stabilized in ambient air using MASCN by strong interaction between ions and strong hydrogen bonds.

One-step synthesis of FA1-xGAxPbI3 perovskites thin film with enhanced stability of alpha (α) phase

In this work, formamidinium lead iodide (FAPbI3) with different Guanidinium (GA) content (2.5%, 5%, 10% and 20%) were successfully deposited by a spin coating method. The influence of GA incorporation into the FA1-xGAxPbI3 films was studied. The crystal structures, surface morphology and optical properties have been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), photoluminescence and UV–Visible spectrometer, respectively. The crystalline structure of the undesirable δ and desirable α-phase were found in the orientation of (010) and (110) planes at diffraction angles 2 θ = 11.5° and 13.8°, respectively. It is observed from the XRD results that the GA content plays an important role in the formation of α/δ phases and stabilization of the α-FAPbI3 phase. Herein, the 10% GA is an adequate amount for FA1-xGAxPbI3 lead to a homogenous, stable α-phase, rough surface, large in grain size and formation of pinhole-free perovskite film. The optical analysis revealed that by increasing the GA content decrease the band gape to lower energy from 1.75 to 1.41 eV. Furthermore, after 15 days the stability of 10% GA was found that remained excellent in a ~60% humid environment. The obtained results indicated that the incorporation of GA into FAPbI3 films makes it promising candidates for photovoltaic application.

Effect of the Crystallization Conditions on the Exclusion/Inclusion Balance in Biodegradable Poly(butylene succinate-ran-butylene adipate) Copolymers.

Biomedical applications of polymers require precise control of the solid-state structure, which is of particular interest for biodegradable copolymers. In this work, we evaluated the influence of crystallization conditions on the comonomer exclusion/inclusion balance of biodegradable poly(butylene succinate-ran-butylene adipate) (PBSA) isodimorphic random copolymers. Regardless of the crystallization conditions, the copolymers retain their isodimorphic character, displaying a pseudo-eutectic behavior with crystallization in the entire composition range. This illustrates the thermodynamic nature of the isodimorphic behavior for PBSA random copolymers. However, depending on the composition, the crystallization conditions affect the exclusion/inclusion balance of the comonomers. Fast cooling favors butylene adipate (BA) inclusion inside the poly(butylene succinate) (PBS) crystals, whereas isothermal crystallization strongly limits it. PBA-rich compositions behave differently. Both fast and slow crystallization formed the β-phase, whereas BS unit inclusion is favored independently of the cooling conditions. During successive self-nucleation and annealing, the BA inclusion is intermediate between non-isothermal and isothermal conditions, while the crystalline structure of the PBA phase changes from the β-phase to the more stable α-phase. We propose a simple crystallographic model to explain the changes in the unit cell dimension of the copolymers.

Structure and Properties of Nonwoven Materials Obtained by Electrospinning of a Solution and Melt of Polyamide-6

Nonwoven materials were obtained by electrospinning a solution and melt of polyamide-6; the average fiber diameter during solution spinning was 0.8–4.5 μm, and during melt spinning, 1.5–7.6 μm. It has been established that during electrospinning (both solution and melt) of polyamide-6, a transition occurs from a stable monoclinic α-phase to a metastable pseudohexagonal γ-phase. Annealing of nonwoven fabrics leads to gradual restoration of the original crystal structure of polyamide in materials obtained from the melt, while for materials formed from a solution, changes after annealing are minimal. It has been found that nonwoven fabrics exhibit hydrophobic properties after production, but lose them after being immersed in water. The sorption capacity of the materials for motor oil is 42–81 g/g, and the residual oil content after desorption does not exceed 4 g/g.

Co-solvent induced piezoelectric γ-phase nylon-11 separator for sodium metal battery

Nylon-11, the most studied member of the odd-numbered nylon family, is a promising functional material for future electronic devices or energy storage systems. To utilize nylon-11 in those applications, it is necessary to control the formation of the applicable metastable crystal phases such as the piezoelectric γ-phase or ferroelectric δ′-phase. Herein, we describe a facile method of fabricating metastable γ-phase nylon-11 fibers via electrospinning with a tailored solvent system. By using a solvent mixture of 1,1,1,3,3,3-hexafluoro-2-propanol and trifluoroacetic acid [HFIP:TFA (75:25 mol%)], we could fully eliminate the formation of the most stable α-phase and create metastable γ-phase nylon-11 fibers. The electrospun γ-phase nylon-11 fibrous membrane displayed a typical piezoelectric response when it experienced a periodic external force. Furthermore, the γ-phase nylon-11 fibrous membrane exhibited higher thermal stability, electrolyte wettability, and ionic conductivity than the conventional Celgard separator. Consequently, it achieved decent performance when applied as a separator in a sodium metal half-cell. This study indicates that piezoelectric γ-phase nylon-11 fibrous membranes have great potential for further development in energy harvesting and storage, especially as piezo-separators in self-charging power cells.

Green fluorescence from perylene liquid in the molten state

Green fluorescence from perylene liquid in the molten state was observed, which differed substantially from the orange fluorescence from the sandwich excimer generally observed in concentrated solutions and in stable α-phase crystals. The peak position of the green fluorescence was similar to those in unstable β-phase crystals and in densely doped polymer films. Results from analysis of spectral components indicate that the green fluorescence is emitted from an excimer with non-parallel geometry, populated by thermal activation of the excimer with sandwich geometry.

Comparative study of phase transformation of Al2O3 nanoparticles prepared by chemical precipitation and sol-gel auto combustion methods

Al2O3 nanoparticles were prepared by Chemical Precipitation (CP) and Sol-Gel Auto Combustion (SGAC) methods and a comparative study on structural behaviour of the nanoparticles was carried out. Nanoparticles prepared by CP gradually transformed to the thermodynamically stable α-phase of alumina at an annealing temperature of 1100 °C whereas pure α-alumina directly obtained for the nanoparticles prepared by sol gel method during the combustion stage. Surface morphology showed the agglomeration of particles after calcining at a higher temperature. Nanoparticles prepared by SGAC method at low temperature showed the same thermal behaviour as those annealed at 1100 °C after being prepared by CP method.

Increasing α-phase content of alumina-chromia coatings deposited by suspension plasma spraying using hybrid and intermixed concepts

The novel method of hybrid suspension plasma spraying of dry coarse aluminum oxide powder with chromium oxide suspension using hybrid water/argon-stabilized (WSP-H 500) plasma torch was utilized for the deposition of coatings with very high α-phase content reaching up to 90%. The deposition mechanism and phase composition were compared with those of coatings deposited from i) intermixed alumina-chromia suspension and ii) alumina suspension doped with chromium nitrate nonahydrate solution. All deposition routes showed alternative ways of preparation of novel multimaterial coatings. It was demonstrated that the chromia addition and the deposition route play the crucial role in the pronounced formation of the thermodynamically stable α-phase.

Nanostructure Changes in Nylon 5,6 Fibers under Tension owing to Hydrogen Bond Formation

We investigated the effect of tension on the stable α-phase formation of nylon 5,6 fibers with two different drawing speeds using two-dimensional transmission wide angle X-ray scattering (2D WAXS) measurement. In an ex-situ condition, i.e., after releasing the applied tension and temperature, the relative amount of the α-phase in the fibers was higher at a higher drawing speed (57 mm/min). On the contrary, the development of the α-phase seemed faster and stronger during in-situ elongation of the fiber at a lower drawing speed (38 mm/min). The γ-phase, rather than the α-phase, played a key role in this complex behavior. The mechanical properties of the nylon fibers elongated under slow drawing speed (38 mm/min) were better than those elongated under a higher drawing speed (57 mm/min). The mechanical properties were more consistent in the case of α-phase formation in an in-situ condition under applied tension on the nylon fibers. Detailed structural information was obtained by quantitative analysis of the 2D WAXS data using an in-situ fiber drawing device.

Low-Temperature Stable α-Phase Inorganic Perovskite Compounds via Crystal Cross-Linking.

Inorganic perovskite compounds hold promise to improve the stability of perovskite solar cells (PSCs). However, the phase instability and high annealing temperature process of these metastable structural polymorphs such as α-phase CsPbI3- xBr x hinder their further development. Herein, we demonstrated the successful reduction of temperature from 250 to 100 °C during the growth of stable and high-crystallinity α-phase CsPbI2Br via crystal cross-linking. 4-Aminobenzoic acid (ABA) was used as a nonvolatile additive with slight solubility in water to bridge the adjacent CsPbI2Br to form a grain-interconnected film. The interaction between ABA and perovskite grains leads to the growth of highly crystalline perovskite films. The optimized PSC based on ABA-incorporated CsPbI2Br using a TiO2/Al2O3/NiO/carbon architecture exhibits an efficiency of 8.44%. More importantly, the additive enables significant improvement of phase stability against moisture. The good performance highlights the chemical modification via cross-linking to achieve efficient and stable inorganic perovskite devices.

Effect of High Pressure and Temperature on Magneto-Electronic, Thermodynamic, and Transport Properties of Antiferromagnetic HoPdX (X = As, Ge) Alloys

We present electronic, magnetic, thermoelectric, and thermodynamic properties of half-Heusler HoPdAs and HoPdGe materials in stable α-phase. They crystallize in cubic MgAgAs-type structure. The stable phase is found to be antiferromagnetic in comparison to the other magnetic and nonmagnetic states. The electronic structure calculations display the metallic behavior in both spin states. The effect of pressure and temperature on unit cell volume, thermal expansion coefficient, heat capacity, and Gruneisen parameter have also been analyzed using the quasi-harmonic Debye model. The alloys present a high absolute Seebeck coefficient with a value of 203.26 μV/K for HoPdAs and 53.19 μV/K for HoPdGe at room temperature.

Optimal Design of High-Strength Ti‒Al‒V‒Zr Alloys through a Combinatorial Approach

The influence of various Zr contents (0–45 wt.%) on the microstructure and mechanical properties of Ti6Al4V alloy was investigated through a combinatorial approach. The diffusion multiples of Ti6Al4V–Ti6Al4V20Fe–Ti6Al4V20Cr–Ti6Al4V20Mo–Ti6Al4V45Zr were manufactured and diffusion-annealed to obtain a large composition space. Scanning electron microscopy, electron probe micro-analysis, and a microhardness system were combined to determine the relationships among the composition, microstructure, and hardness of these alloys. The Ti–6Al–4V–30Zr alloy was found to contain the thinnest α lath and showed peak hardness. X-ray diffraction and transmission electron microscope results indicated that after quenching from the β-field, the metastable α″-phase formed; moreover, at the secondary aging stage, the metastable α″-phase acted as precursor nucleation sites for the stable α-phase. The bulk Ti6Al4V30Zr alloy was manufactured. After aging at 550 °C, the alloy showed excellent balance of strength and ductility, and the tensile strength was 1464 MPa with a moderate elongation (8.3%). As the aging temperature increased, the tensile strength and yield strength of the alloys rose, but the total elongation decreased. The lamella thickness and volume fraction of the α-phase were the major factors that had great impacts on the mechanical properties.

<i>In Situ</i> Observation of the Phase Transformations in Ti15Mo Alloy Deformed by High Pressure Torsion

Metastable β-Ti alloys including Ti15Mo alloy are perspective candidates for use in medical applications. During thermal treatment Ti15Mo alloy undergoes various phase transformations. After solution treatment it contains metastable β-phase and ω-phase. During annealing the ω-phase partially dissolves as well as stable α-phase particles are formed. The solution treated Ti15Mo alloy was deformed by high pressure torsion (HPT) at room temperature. Significant grain refinement with grain size of ~100 nm was achieved even after 1/4 of HPT rotation. The effect of the ultra-fine grained (UFG) structure achieved by HPT on the phase transformations was studied by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) during in-situ heating. High density of lattice defects, dense network of grain boundaries as well as ongoing recovery and recrystallization upon heating significantly affected the phase transitions. Observation of the microstructure during in-situ heating in TEM revealed no representative changes in transparent part of the sample due to the “thin foil effect”.

Solvent-controlled growth of inorganic perovskite films in dry environment for efficient and stable solar cells

Inorganic halide perovskites such as cesium lead halide are promising due to their excellent thermal stability. Cesium lead iodide (CsPbI3) has a bandgap of 1.73 eV and is very suitable for making efficient tandem solar cells, either with low-bandgap perovskite or silicon. However, the phase instability of CsPbI3 is hindering the further optimization of device performance. Here, we show that high quality and stable α-phase CsPbI3 film is obtained via solvent-controlled growth of the precursor film in a dry environment. A 15.7% power conversion efficiency of CsPbI3 solar cells is achieved, which is the highest efficiency reported for inorganic perovskite solar cells up to now. And more importantly, the devices can tolerate continuous light soaking for more than 500 h without efficiency drop.

Spark Stage of Welding Arc Discharge Binding on an Aluminum Surface

The article presents a study of the spark stage of binding of the welding arc discharge on the surface of aluminum covered by oxide film. The experiments have shown the formation of cathode- and anodedirected leaders in a nonuniform field between the pin cathode (tungsten) and the plate (aluminum). It has been found that, if the cathode spot occurs against the background of uniform discharge glow, then the spark channel forms, as a rule, in two stages. At the first stage, a diffuse channel bound to the cathode spot that forms in the gap. At the second stage, a highly conductive contracted spark channel spreads from the cathode side along the diffuse channel; the brightness of that spark channel is comparable to that of the cathode plasma glow. From the color spectrum, it has been found that intensive aluminum emission takes place in the domain of binding spots already at the stage of avalanche-streamer spark formation. The estimated calculation of the heat flux rate in the binding spot of the spark discharge has shown values of 106–108 W/cm2, i.e., comparable to laser heating parameters. The spark discharge exerts a significant thermal impact consisting of melting of the surface in the spark binding zone and the development of the recrystallization process of an amorphous film matrix in the zone of thermal effect. Electron diffraction through the thin film layer in the thermal effect zone has shown clear concentric rings corresponding to the polycrystal γ-phase of Al2O3. According to transmission electron microscope data, the average size of γ-phase grains in the surface film layer after impact by the spark is d = 8–15 nm, whereas the volume of the produced γ-phase is at least 70%. The stable thermodynamic α-phase in the melting zone has been fixed. By the moment of arc discharge excitation, the entire aluminum surface in the spark-binding zone has been free of oxide film.

TL/OSL properties of beta irradiated Al2O3:Tm3+ phosphor synthesized by microwave combustion method

This work discusses synthesis of stable α-phase of Al2O3:Tm3+ by combustion method using temperature controlled microwave oven. The crystalline phase was analyzed by X-ray diffraction (XRD) technique and average crystallite size was found to be 147 nm. Observations using scanning electron microscope (SEM) image suggest formation of agglomerated particles and energy dispersive x-ray spectroscopy (EDS) confirmed the incorporation of Tm3+ in Al2O3. Thermoluminescence emission (TLE) spectrum of γ – irradiated Al2O3:Tm3+ shows characteristic emissions of Tm3+, Cr3+ and Mn4+. TL glow curves of γ – irradiated Al2O3:Tm3+ exhibit a prominent peak at 453 K along with a shoulder at 496 K. The glow curves of β – irradiated Al2O3:Tm3+ were studied in different emission regions using U340 + BG39 (UV band pass), CS759 + BG39 (Blue band pass) and BG39 (Visible band pass) optical glass filters. A prominent peak was observed at 471 K in for all mentioned emission regions and an additional shoulder was observed at 511 K with CS759 + BG39 and BG39 filters. TL glow curve of β – irradiated Al2O3:Tm3+ using only BG39 filter had more counts than CS759 + BG39 and U340 + BG39 filters. Further, the effect of Tm3+ impurity on TL response was studied. TL kinetic parameters were estimated by using computerized glow curve deconvolution (CGCD) technique. The activation energy and frequency factor of prominent peak (471 K) were found to be 1.31 eV and 3.50 × 1013 s−1 respectively. Optically stimulated luminescence (OSL) characteristics of β – irradiated Al2O3:Tm3+ were studied using U340 + BG39 and CS759 + BG39 filters. Highest OSL intensity was observed in UV. OSL curves were deconvoluted by general order decay equation. Life time and photoionization cross section of the traps responsible for OSL were found to be 5.30 s and 3.98 × 10−18 cm2 respectively. The process of ionization of electron from Tm3+, electron trap in host lattice and its recombination mechanism is proposed. Phosphorescence decay of beta irradiated sample was also studied. The lifetime of phosphorescence decay was found to be 140 s for the prominent peak and TL intensity decays 25% after the phosphorescence. TL/OSL dosimetric properties viz. linearity with dose, reusability and minimum detectable dose of the phosphor were characterized for medical dosimetry application.

Nanoscale Investigations of α- and γ-Crystal Phases in PVDF-Based Nanocomposites.

The impact of carbon nanotube (CNT) incorporation into semicrystalline poly(vinylidene fluoride), PVDF, was investigated at both the macro and nanoscales. A special effort was devoted to probe the local morphology and the mechanical, ferroelectric, piezoelectric, and electrical conductivity response by means of atomic force microscopy. Incorporation of CNTs mainly induces the development of the polar γ-phase, and as a consequence, the coexistence of the γ-phase with the most stable nonpolar α-phase is observed. A maximum γ-phase content is reached at 0.7 wt % CNT loading. The spherulitic morphology of the PVDF α-phase is assessed, in conjunction with the lack of any ferroelectric response, while the presence of the polar γ-phase is confirmed, owing to clear piezoresponse signals. Local piezoelectric measurements on γ-phase domains yield a maximum effective coefficient | d33| ≈ 13 pm/V, thus underlining the potential for applications of such functional PVDF-based nanocomposites in advanced piezoelectric devices. An increase in macroscopic conductivity with CNT content is observed, with a percolation threshold achieved for a composition close to 0.7 wt %. Nanoscale investigation of the electrical conductivity confirms the presence of some infinite CNT cluster homogeneously distributed over the surface. The macroscopic viscoelastic behavior of the composite reflects the reinforcing effect of CNTs, while the nanomechanical characterization yields a local contact modulus of the γ-phase domains larger than that of its α-phase counterpart, in agreement with the fact that the CNTs act as γ-phase promoters and subsequently reinforce the γ-domains.

Atomistic evolution during the phase transition on a metastable single NaYF4:Yb,Er upconversion nanoparticle

The phase evolution of as-prepared NaYF4:Yb,Er upconversion nanoparticles (UCNPs) with a metastable cubic structure is studied based on in situ heating experiments via transmission electron microscopy (TEM). The atomistic behavior on the single NaYF4:Yb,Er UCNP is observed during the phase transition. The formation and evolution of voids on the NaYF4:Yb,Er UCNP appear at a temperature below 420 °C. Small circular voids are transformed at the initial stage to a large, hexagonal-pillar shaped single void. Two different routes to reach the stable α-phase from the metastable cubic structure are identified on a single NaYF4:Yb,Er UCNP. The first is via a stable β-phase and the second is a direct change via a liquid-like phase. The specific orientation relationships, [110]cubic//[11bar{2}0]hexagonal and {002}cubic//{2bar{2}00}hexagonal, between the cubic and hexagonal structures are confirmed. Additionally, a few extra-half planes terminated in the cubic structures are also observed at the cubic/hexagonal interface.

Effect of monopalmitic content and temperature on precipitation rate in biodiesel-petroleum diesel blends

The need for cleaner fuel increases alongside the necessity of reducing greenhouse gas emissions. Biodiesel is considered as one of best options for cleaner energy. However, it has disadvantages due to lower stability, lesser cold flow properties (CFP), and higher viscosity, which are mainly caused by fatty acid type and content. These works investigate CFP of various biodiesel blends B20 & B30, with the objective on how the monopalmytic as one of the saturated monoglycerides (SMG) content and Temperatures affect the precipitation rate. A set of 100ml separatory funnels containing various samples were put in refrigerators in controlled-temperature, i.e.15°C; 20°C; and room temperature. The rate of precipitation was observed every day for 2 weeks using 0.8μm membrane filter. Results indicated precipitation rate of B30 was higher than that of B20. As it was expected, the precipitate was taken at the same temperature, 20°C, resulting in B30 had more precipitate in the end (37.6 mg) compared to B20 (22.2 mg). The closer to cloud point also indicates the higher rate of precipitation as 4th day B20 at 15°C (25.4 mg) compared 4th day B20 at 20°C (19.3 mg). The change of crystal from less stable α-phase to more stable, less soluble β-phase is also proven to significantly affect the rate of precipitation.