Predominant Crystal Phase Research Articles

Hydrothermal Approach of Spinel Copper Cobaltite (CuCo2O4) Nanostructures and Their Structural and Functional Properties

CuCo2O4 nanoparticles were synthesized via facile hydrothermal route using oxalic as a precipitant, thermal decomposition of CuCo2O4 precursor at 400[Formula: see text]C. The structural studies from X-ray diffraction (XRD), Fourier transform infrared spectrometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) disclose the predominant spinel crystal phase for copper cobaltite. The optical absorption spectra reveal two band gaps of 3.8[Formula: see text]eV and 4.4[Formula: see text]eV in the CuCo2O4 nanoparticles. The cyclic voltammetry (CV) was used to assess the electrochemical characteristics of the resulting product in an organic electrolyte at −1.5–1.5[Formula: see text]V under ambient conditions. On 22.4[Formula: see text]nm CuCo2O4 nanoparticles, a greater capacitance of 920[Formula: see text]F/g at a scan rate of 5[Formula: see text]mV/s was achieved.

Pyrolysis of hyphaene thebaica shell over ceramic tile dust-derived catalysts and assessment of the produced bio-oil

The purpose of this study is to demonstrate the potential of ceramic tile dust (CTD)-derived ZSM-5 zeolite (CZ) and its monodispersed composite with metal oxides (MgO and Fe2O3) in the catalytic pyrolysis of hyphaene thebaica shell (HTS). The HTS was pyrolysed in a Fixed-bed reactor at 400–600 °C, and 100–300 mL/min N2 flowrate. The maximum bio-oil production of 32 % was obtained at 500 °C and 150 mL/min N2 flowrate, with bio-oils containing 50 % acid and octadecenoic acids, as well as esters, phenols, aldehydes, ketones, ethers, aromatics, and hydrocarbons. A carboxymethyl cellulose templating agent was employed for the mesoporous zeolite synthesis from CTD. This resulted in the mesoporous zeolite with a predominant ZSM-5 crystal phase, exhibiting pore diameters ranging from 1.8-6 nm, 229 m2/g surface area and 1145 μmol/g total acidity. The catalytic pyrolysis of HTS was conducted using the ZSM-5 zeolite (CZ) and metal-oxide (MgO, Fe2O3, and Fe2O3/FeO) modified CZ, as monodispersed composite catalysts. Under best thermal pyrolysis conditions, CZ-Fe2O3, CZ-MgO, and CZ-Fe2O3/MgO demonstrated 22–23 % bio-oil yields. Notably, the CZ-Fe2O3/MgO catalyst exhibited the highest hydrocarbon yield at 16 %, while the CZ-MgO favoured the production of phenolics, esters, and alcohols. CZ-MgO also displayed the highest coking level at 7.5 %, indicating faster deactivation than the other catalysts. The synthesised catalysts exhibited remarkable catalytic activity, resulting in a notable improvement in the quality of bio-oils obtained from the intermediate pyrolysis of hyphaene thebaica shells in a fixed-bed reactor.

Non-isothermal crystallization kinetics of CaO-SiO2-B2O3-TiO2 glass studied by differential thermal analysis in the case of “site saturation”

Crystallization characteristics of the CaO-SiO2-B2O3-TiO2 glass have been studied using scanning electron microscopy, X-ray diffraction and differential thermal analysis techniques. The crystallization kinetic parameters of this glass were estimated under non-isothermal conditions using the Matusuta-Sakka equation. Glass with fine particles (<74 μm), case referred to as ‘‘site saturation’’, was used to obtain the non-isothermal differential thermal analysis curves. Bulk glass-ceramics with dense and nonporous morphology are obtained after the heating treatment indicating the strong heterogeneous nucleation at the junction of gain boundaries in the case of “site saturation”. As the content of TiO2 exceeds 18%, the predominant crystal phase changes from CaSiO3 to CaTiSiO5, until CaTiSiO5 becomes the only crystal phase of the glass at 26% TiO2. The crystallization activation energies, EG, are in the range of 245–514 kJ/mol. As TiO2 increases from 10% to 18%, crystallization ability of the glass decreases gradually and the crystallization corresponds to one-dimensional growth mechanism or surface crystallization, while as TiO2 further increases from 18% to 26%, not only does the glass show an increasing crystallization ability, but also the crystal growth changes to the two-dimensional growth mechanism. Within the range of 22%–26%, TiO2 plays the role of strengthening the crystallization of the glass by acting as a major component in the glass to form Ti-bearing compound. From the standpoint of glass-ceramics preparation, the glass containing more TiO2 (such as 26%) with CaTiSiO5 as the only crystal phase is favorable in the present study.

Performance evaluation for Ag and Au nanoparticle containing K 2 O‐MgO‐B 2 O 3 ‐Al 2 O 3 ‐SiO 2 ‐F glass sealants for SOFC application

Performance evaluation for Ag and Au nanoparticle containing K ₂ O‐MgO‐B ₂ O ₃ ‐Al ₂ O ₃ ‐SiO ₂ ‐F glass sealants for SOFC application

Parameters to be considered for the development of highly photoactive TiO2 layers on aluminium substrates by RF magnetron sputtering for treating polluted air

In this study, photoactive titanium dioxide films deposited on aluminium substrates using Radio-Frecquency (RF) magnetron sputtering have been developed, with the goal of advancing this technology for indoor air treatment. With this goal in mind, the influence of deposition parameters, namely post annealed heat treatment, working pressure and deposition time, on the physico-chemical properties of the layers has been studied. Photocatalytic efficiency for trichloroethylene degradation in gas phase, and self-cleaning performance of the developed materials have been evaluated. Samples have been thoroughly examined using different techniques (SAXRD, UV-Vis, SEM-EDX, contact angle, profilometry, hardness, among others) in order to determine the structural-photocatalytic relationship. The findings indicate that high-temperature annealing promotes the diffusion of alumina, copper and iron ions towards the surface of the samples resulting in the formation of aluminium alloys. These alloyed species can act as recombination centres adversely affecting the photocatalytic activity. The sputtering pressure also affects the nature of the titanium phases formed during the sputtering. Increasing the thickness of the TiO2 layer leads to rougher surfaces with TiO2-anatase as the predominant crystal phase. Annealing temperatures of 350 °C, argon pressures between 0.8 and 1.0 Pa, and TiO2 layer thickness of ca. 110 nm are the optimal conditions to prepare well-adhered TiO2 layers with high photocatalytic performance. UV-A photoinduced superhydrophilicity phenomena was observed for all TiO2/Al materials.

Effect of SiO2/Al2O3 Ratio on the Crystallization and Heavy Metal Immobilization of Glass Ceramics Derived from Stainless Steel Slag

This study investigated the effects of the SiO2/Al2O3 mass ratio on the glass stability, crystallization and heavy metal immobilization of glass ceramics derived from stainless steel slag (SSS). When the SiO2/Al2O3 mass ratio decreased from 11.2 to 4.2, the glass stability and the depolymerization degree of the parent glass increased from 2.13 to 2.40 and subsequently decreased to 2.31. The predominant crystal phase of the resulting glass–ceramics changed from pyroxene and diopside to wollastonite, pyroxene, and diopside as the crystallization temperature of samples increased from 800°C to 860°C. The heavy metals, Cr and Mn, from SSS cured in the spinel of glass–ceramics, whereas the hazardous metal Ni was primarily found in pyroxene (CaNiSi2O6). In addition, the leached concentrations of hazardous metals, Ni, Mn, and Cr ions, in glass-ceramics were far below the national standard. The results showed that it is possible and safe to turn SSS into eco-friendly glass-ceramic.

Surface depth-dependent and microstructural analyses of high performance lithium iron silicate with 15% vanadium modification

The surface, interface and microstructure studies were carried out for the nominal 15% vanadium modified carbon coated lithium iron silicate composite in an effort to understand the enhanced electrochemical performance and decayed cycle performance. The empirical formula was determined to be Li2.09Fe0.78V0.22Si1.29O6.29. It was confirmed that the surface of the as-prepared composite was coated by amorphous carbon with the thickness of approximately 50 nm. Furthermore, the predominant crystal phase changed from monoclinic P21 to orthorhombic Pmn21 after the vanadium modification. The simultaneous presences of multivalent iron (Fe) and vanadium (V) ions were identified by performing multi-peak fitting analyses in the depth-dependent X-ray photoelectron spectroscopic spectra of Fe2p and V2p. The detailed microstructure, interface and surface characterizations provided strong evidence that the partial substitution of divalent iron (Fe2+) with divalent vanadium (V2+) in the structure and the surface modification by vanadium might become possible, leading to 29.1% increase in total carbon content, and 35.8% and 41.3% decreases in the interfacial charge transfer resistance and lithium–ion diffusion coefficient, respectively. The faster interfacial charge transfer kinetics greatly enhanced the initial discharge capacity, while the slower lithium–ion diffusion process apparently degraded the cycle performance.

Photocatalytic Inactivation of Plant Pathogenic Bacteria Using TiO2 Nanoparticles Prepared Hydrothermally.

Exploitation of engineered nanomaterials with unique properties has been dynamically growing in numerous fields, including the agricultural sector. Due to the increasing resistance of phytopathogenic microbes, human control over various plant pathogens in crop production is a big challenge and requires the development of novel antimicrobial materials. Photocatalytic active nanomaterials could offer an alternative solution to suppress the plant pathogens. In this work, titanium dioxide nanoparticles (TiO2 NPs) with high photocatalytic activity were synthesized by hydrothermal post-treatment of amorphous titania at different temperatures (250 °C or 310 °C) without using any additives or doping agents. The obtained samples were investigated through X-ray diffraction, N2-sorption measurements, diffuse reflectance UV-Vis spectroscopy, transmission electron microscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The applied hydrothermal treatment led to the formation of TiO2 nanocrystallites with a predominant anatase crystal phase, with increasing crystallinity and crystallite size by prolonging treatment time. The photocatalytic activity of the TiO2 NPs was tested for the photo-degradation of phenol and applied for the inactivation of various plant pathogens such as Erwinia amylovora, Xanthomonas arboricola pv. juglandis, Pseudomonas syringae pv. tomato and Allorhizobium vitis. The studied bacteria showed different susceptibilities; their living cell numbers were quickly and remarkably reduced by UV-A-irradiated TiO2 NPs. The effectiveness of the most active sample prepared at 310 °C was much higher than that of commercial P25 TiO2. We found that fine-tuning of the structural properties by modulating the time and temperature of the hydrothermal treatment influenced the photocatalytic properties of the TiO2 NPs considerably. This work provides valuable information to the development of TiO2-based antimicrobial photocatalysts.

Plasma Electrolytic Oxidation of Titanium in H2SO4–H3PO4 Mixtures

Oxide layers on titanium foils were produced by galvanostatically controlled plasma electrolytic oxidation in 12.9 M sulfuric acid with small amounts of phosphoric acid added up to a 3% mole fraction. In pure sulfuric acid, the oxide layer is distinctly modified by plasma discharges. As the time of the process increases, rough surfaces with typical circular pores evolve. The predominant crystal phase of the titanium dioxide material is rutile. With the addition of phosphoric acid, discharge effects become less pronounced, and the predominant crystal phase changes to anatase. Furthermore, the oxide layer thickness and mass gain both increase. Already small amounts of phosphoric acid induce these effects. Our findings suggest that anions of phosphoric acid preferentially adsorb to the anodic area and suppress plasma discharges, and conventional anodization is promoted. The process was systematically investigated at different stages, and voltage and oxide formation efficiency were determined. Oxide surfaces and their cross-sections were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The phase composition was determined by X-ray diffraction and confocal Raman microscopy.

Tantalum-based electrocatalysts prepared by a microemulsion method for the oxygen reduction and evolution reactions

Bifunctional catalysts for oxygen electrodes, active for both the oxygen reduction and evolution reactions (ORR, OER), are highly desirable for the development of electrochemical energy conversion devices. In this work, carbon-supported tantalum based catalysts were synthesized by a microemulsion procedure from tantalum ethoxide through a fast hydrolysis reaction followed by heat treatment. The nature and composition of the different tantalates and oxides (general formula NaaTabOc, with a/b = 0–1 and c/b = 2.5–3) relied on the concentration of ethanol as well as on the annealing temperature, with Na2Ta8O21 as predominant crystal phase in all cases. High annealing temperatures resulted in a certain degree of oxygen substoichiometry, which creates defects responsible of electrocatalytic activity. The electrochemical response for the oxygen reduction and the oxygen evolution reactions in alkaline electrolyte (0.1 M NaOH) was evaluated for the first time in this type of materials. The presence of Na2Ta8O21 phase over other oxides/tantalates, a high crystallinity of such Ta-phase, and the oxygen substoichiometry are the three parameters playing a relevant role to favor ORR and OER electro-activity. The best formulations were found in a trade-off situation using 3% ethanol and annealing at 900 °C.

Catalytic activity of nanocrystalline ZnM2O4 (M = Fe, Co) prepared via simple and facile synthesis of thermal decomposition of mixed metal complexes of Schiff bases generated from α-ketobutyric acid and diaminoguanidine

Metal complexes ([ML2], where M = Fe, Co, or Zn; HL = 2-[(6-ethyl-5-oxo-4,5-dihydro-2H-[1,2,4]triazin-3-ylidene)-hydrazono]-butyric acid, C9H13N5O3) of a Schiff base derived from α-ketobutyric acid (α-KBA) and diaminoguanidine (Damgu) were synthesized and characterized using elemental, spectral, and thermal studies. The metal complexes exhibited similar decomposition behavior, with a highly exothermic final decomposition step resulting in the formation of metal oxides. Isomorphism among the complexes was revealed using a powder X-ray diffraction (PXRD) technique. Solid solution precursors ([Zn1/3M2/3(L)2], where M = Fe, Co) were synthesized and characterized using various physico-chemical techniques. A thermal decomposition technique was used to prepare spinel-type zinc cobaltite (ZnCo2O4) and zinc ferrite (ZnFe2O4) nanocrystalline particles with the synthesized single source precursors. Structural studies using PXRD ascertained the predominant crystal phase to be spinel. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed a mean nanoparticle size of 18 ± 2 nm. Magnetic measurements revealed a weak magnetic behavior in the synthesized spinels. In the aqueous phase, the spinels exhibited catalytic activity, reducing 4-nitrophenol (4-NP) in the presence of NaBH4 at room temperature. Additionally, the study demonstrated that the catalyst can be recovered and reused for five cycles with a more than 85% conversion efficiency.

Enhanced optical properties of spherical zirconia (ZrO2) nanoparticles synthesized via the facile various solvents mediated solvothermal process

The influence of various solvents on structural and optical properties of zirconia (ZrO2) nanoparticles was successfully synthesized by via the facile solvothermal process at mild temperature of 180 °C. The aims of this study were to identify how the solvents selection affects particle size and properties of the prepared materials. Structural characterization of the ZrO2 products using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the predominant crystal phase was the monoclinic phase. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images display particles of spherical shapes in nature and size of diameters in the range of 5–6.5 nm. By changing the solvent, we observed variations in particle size. The optical properties of the products were studied by ultraviolet–visible (UV–Vis) and photoluminescence (PL) emission spectroscopy, which was confirmed that the prepared ZrO2 nanoparticles are promising good candidate inorganic material for optoelectronics applications and new lighting devices. Furthermore, we discussed the mechanism of the solvothermal process and the critical roles of boiling point of solvents in the solvothermal formation of the small-sized ZrO2 nanoparticles.

Effect of thermal annealing sequence on the crystal phase of HfO2 and charge trap property of Al2O3/HfO2/SiO2 stacks

In this study, we investigated the effect of a post annealing sequence on the HfO2 crystal phase and the memory window of charge trap devices with TiN-Al2O3-HfO2-SiO2-Si stacks. The charge trap dielectrics of HfO2 were deposited by atomic layer deposition and were annealed in an oxygen environment with or without Al2O3 blocking oxides. X-ray diffraction analysis showed that, after thermal annealing, the predominant crystal phase of HfO2 is divided into tetragonal and monoclinic phase depending on the presence or absence of Al2O3 blocking oxide. In addition, deconvolution of X-ray diffraction spectra showed that, with increasing annealing temperature, the fraction of the tetragonal phase in the HfO2 film was enhanced with the Al2O3 blocking oxide, while it was reduced without the Al2O3 blocking oxide. Finally, measurements of program/erase and increase-step-pulse programming showed that the charge trap efficiency and the memory window of the charge trap devices increased with decreasing fraction of tetragonal HfO2.

The influence of MgF2 content on the characteristic improvement of machinable glass ceramics

The influence of MgF2 on the various properties like crystalline behavior, microstructure phases, hardness etc. in the SiO2–Al2O3–MgO–K2O–B2O3 glass system has been investigated. Three batches of glass system were synthesized and characterized by differential scanning calorimetry (DSC), coefficient of thermal expansion (CTE), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) equipped with energy dispersion X-ray spectroscopy (EDS). DSC study reveals that with the increase in MgF2 content the glass transition temperature (Tg) and first crystallization peak temperature (TpI) decreased whilst the second crystallization peak temperature (TpII) slightly increased. The CTE of the glasses is found to be in the ranges 6.34–6.40×10−6K−1 (50–400°C). The activation energy (Ec) and frequency factor (υ) both increase with increasing MgF2 content. The three-dimensional crystal growth is observed. The mica crystals are identified as fluorophlogopite, the predominant crystal phase for all the three glass specimens heat treated at 1050°C. Vickers hardness values decrease with increasing amount of fluorine content and it gives better machinability.

Memristive devices from porous silicon – ZnO/VO2 nanocomposites

As metal oxides act as an active media for oxygen vacancies transport after their infiltration/confinement in the submicron porous structure, we report the memristive device fabrication from nanostructured porous silicon – metal oxide (ZnO and VO2) composites. Scanning electron microscopy and X-ray diffraction were used for morphological and structural characterization, respectively. Predominant crystal phase of metal oxides was found to be wurtzite for ZnO and monoclinic for VO2. Electrical characterization reveals that both devices present symmetrical zero-crossing pinched hysteresis curves, typical of memristive systems. Although both the devices reveal significant endurance and stable switching ratio, ZnO-based device exhibits relatively better stability and 86% higher resistive switching ratio with respect to VO2-based device. The proposed memristive devices have potential applications as practical and economical structures that could be integrated in current silicon based microtechnology.

Optical characterization of sol–gel ZnO:Al thin films

This work presents a sol–gel approach for ZnO:Al films deposition. The effect of Al component and annealing treatments (from 500 to 800°C) on the film structural and optical properties has been studied. Sol–gel ZnO and Al2O3 films are used for comparative analyses. Structural evolution as a function of annealing temperatures is investigated by using X-ray diffraction (XRD). XRD analysis of ZnO:Al films revealed that the predominant crystal phase is a wurtzite ZnO. It can be seen that the addition of Al leads to decaying of the film crystallinity. Fourier Transform Infrared (FTIR) and UV–VIS spectrophotometry are applied for characterization of the vibrational and optical properties. The Al component influences the shapes of the absorption bands. The optical properties of the sol–gel ZnO, ZnO:Al and Al2O3 films reveal very interesting features. Increasing Al component results in significantly higher film transparency.

Crystallization Kinetics of CaO-SiO&lt;sub&gt;2&lt;/sub&gt;(CaO/SiO&lt;sub&gt;2&lt;/sub&gt;=1)-TiO&lt;sub&gt;2&lt;/sub&gt;-10 mass%B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Glassy Slag by Differential Thermal Analysis

Crystallization characteristics of the CaO-SiO2-TiO2-10%B2O3 glassy slag at w(CaO)/w(SiO2)=1 have been studied by Differential Thermal Analysis (DTA) and Matusita-Sakka method. Crystallization products have been distinguished by employing X-ray diffraction (XRD) and Scanning Electron Microscopy equipped with Energy Dispersive Spectroscopy (SEM-EDS). As the TiO2 content is within 10-18%, the crystal phase precipitated is mainly CaSiO3, and the effective activation energies for crystal growth increase with the increase of TiO2 content. Crystallization mechanism for CaSiO3 shifted from surface crystallization to one-dimensional growth with increase of TiO2. As the TiO2 content in slag further increases to 22% and 26%, CaTiSiO5 becomes the predominant crystal phase precipitated, and the effective activation energies for crystal growth decrease with the increase of TiO2 content. Crystallization mechanism for CaTiSiO5 is mainly surface crystallization. Therefore, with the increase of TiO2 content, the crystallization ability of the CaO-SiO2-TiO2-10%B2O3 glass system decreases initially and then increases.

Preparation of TiO2 nanoparticles by the sol–gel method under different pH conditions and modeling of photocatalytic activity by artificial neural network

In this study, TiO2 nanoparticles were prepared by the sol–gel method under different pH conditions and the structural properties of TiO2 nanoparticles were obtained by X-ray diffraction and transmission electron microscopy. The photocatalytic activity of TiO2 nanoparticles was studied in the removal of C.I. Acid Red 27 (AR27) under UV light. The desired gelation pH for photocatalytic removal of AR27 was obtained at pH 5. At this pH, the predominant crystal phase of TiO2 is anatase and its crystallite size is smaller than at other gelation pHs. The artificial neural network (ANN) technique was applied to model and predict the photocatalytic activity of TiO2 nanoparticles prepared at the desired gelation pH. Four effective operational parameters were inserted as the inputs of the network and reaction rate constants (kap) were introduced as the outputs of the network. The results showed that the predicted data from the designed ANN model are in good agreement with the experimental data with a correlation coefficient (R2) of 0.9852 and mean square error of 0.00242. The designed ANN provides a reliable method for modeling the photocatalytic activity of TiO2 nanoparticles under different operational conditions. Furthermore, the relative importance of each operational parameter was calculated based on the connection weights of the ANN model. The initial dosage of TiO2 nanoparticles was the most significant parameter in the photocatalytic removal of AR27, followed by the UV-light intensity and initial AR27 concentration.

Effect of Na2O and heat-treatment on crystallization of glass–ceramics from phosphorus slag

Na2O–CaO–Al2O3–SiO2–MgO glass was prepared from phosphorus slag as the raw materials and subsequently converted to glass–ceramics. The effects of both heat-treatment system and Na2O content on crystallization and microstructure were investigated by XRD and SEM. For the glass–ceramics with 15 mass% Na2O (A), Na2Ca2Si3O9 appears initially at 850°C, then the dominant β-CaSiO3 from 850°C to 1050°C, which further transforms into α-CaSiO3 from 1050°C to 1150°C. The existing phases are α-CaSiO3 and Na2Ca2Si3O9 at above 1150°C. For the glass–ceramics with 17 mass% Na2O (B), the primary and second phases are β-CaSiO3 and Na2Ca2Si3O9 in the range of 750°C–950°C, respectively. The transformation from β-CaSiO3 to Na2Ca2Si3O9 occurs from 950°C to 1050°C. Na2Ca2Si3O9 gradually transforms into Na2Ca2Si3O9 solid solution from 1050°C to 1150°C, and Na2Ca2Si3O9 solid solution becomes the predominant crystal phase above 1150°C. Surface crystallization is dominant mechanism in glass–ceramics A, while volume crystallization mechanism is predominant in glass–ceramics B.

Preparation of Glass-Ceramic Materials from Rare Earth Tailings

Glass-ceramics materials based on rare earth tailings were prepared by conventional molten cooling method and crystallization process. The composition of the matrix glass was determined by the phase diagram of CaO-Al2O3-SiO2and up to 60 wt% rare earth content was utilized. The phase composition and microstructure of the prepared glass-ceramics materials was tested and observed by DSC, XRD and SEM. The results show the predominant crystal phase of the prepared glass-ceramics is calcium silicate when crystallization temperature ranges from 950°C to 1050 °C. When crystallization temperature is 950°C, a large number of glass phase and spherical crystal with size of 20um coexisted. While the crystalline phase of calcium silicate turned to lamellar from spherical and glass phase disappeared when treating temperature increased to 1050°C.