Major Crystalline Phase Research Articles

Fabrication of self-branched TiO2 nanotubes by anodization method, ordering and crystallinity

This paper reports on the self-branching of TiO2 nanotubes during anodization of Ti metal carried out at a fixed applied potential. These nanotubes are prepared by a two-step anodization carried out in an aqueous electrolyte containing ethylene glycol and ammonium fluoride at a range of anodization voltages of 30–60 V. The self-branching of nanotubes is more pronounced in the first-step anodization than during the second-step anodization at each voltage studied. The nanopits on the titanium surface, exposed after the dissolution of the oxide layer formed in the first-step anodization are observed to be highly regular and uniform. These nanopits provide nucleation sites producing less branched arrays during second step of anodization. Moreover, symmetric pits also result in straight tubes from top to bottom. Considering different applied voltages, the TiO2 nanotubes prepared at 50 V are comparatively more uniform and tend to grow straighter, whereas, numerous turns and pore branching are observed at other applied voltages. In this way, the best order in the tube arrays is found at anodization voltage of 50 V shown by the quantitative analysis as well. In addition, the nanotubes prepared by second-step anodization have shown higher crystallinity and with anatase as the major crystalline phase.

Crystal structures of tricalcium citrates

The crystal structures of calcium citrate hexahydrate, calcium citrate tetrahydrate, and anhydrous calcium citrate have been solved using laboratory and synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Both the hexahydrate and tetrahydrate structures are characterized by layers of edge-sharing Ca coordination polyhedra, including triply chelated Ca. An additional isolated Ca is coordinated by water molecules, and two uncoordinated water molecules occur in the hexahydrate structure. The previously reported polymorph of the tetrahydrate contains the same layers, but only two H2O coordinated to the isolated Ca and two uncoordinated water molecules. Anhydrous calcium citrate has a three-dimensional network structure of Ca coordination polyhedra. The new polymorph of calcium citrate tetrahydrate is the major crystalline phase in several commercial calcium supplements.

Structure, phase evolution, and mechanical properties of DC, pulsed DC, and high power impulse magnetron sputtered Ta–N films

The microstructural development of reactively sputter-deposited tantalum nitride thin films is investigated as a function of the N2-to-total-pressure ratio (pN2/pT) and the operating mode of the metallic tantalum cathode; by direct current magnetron sputtering (DCMS), pulsed DCMS, and high power impulse magnetron sputtering (HiPIMS). For all sputtering modes investigated, the phase evolution of the Ta-N films strongly depends on the nitrogen partial pressure, pN2, used when keeping the total pressure, pT, constant at 0.3 or 0.6 Pa. The major crystalline phases identified, with increasing the pN2/pT-ratio, are α-Ta, orthorhombic o-Ta4N, hexagonal close packed (hcp) γ-Ta2N, face-centred cubic δ-TaN, and hcp ε-TaN. Their development is basically determined by the N2 partial pressure present. The deposition rate decreases slowest with increasing pN2 for the HiPIMS mode and fastest for the DCMS mode. The coatings with a dominating γ-Ta2N phase (which could be obtained for pN2 between 0.08 and 0.15 Pa) exhibit the highest hardness with 38.2 ± 4.6 GPa (HiPIMS), 38.0 ± 2.3 GPa (pulsed DCMS), and 40.0 ± 3.8 GPa (DCMS) among all samples studied. Higher pN2 lead to the formation of δ- and ε-TaN phases and a reduction in hardness. Especially, the ε-TaN rich coatings are comparably soft with only ~20 GPa.Based on our results we can conclude that coatings dominated by Ta-rich o-Ta4N or γ-Ta2N phases exhibit the most favourable mechanical properties, according to which the most important pN2-range is between 0.04 and 0.15 Pa, as for higher N2 partial pressures the films undergo a transformation from γ-Ta2N (plus o-Ta4N) into mixed δ- and ε-TaN.

Study of marbles from Middle Atlas (Morocco): elemental, mineralogical and structural analysis

A series of marbles sampled from the region of Middle Atlas (Morocco), are characterized by different complementary spectroscopic techniques. X-Ray fluorescence is used to determine elemental composition of rock while X-Ray diffraction and the Raman spectroscopy are used to determine major crystalline phases (calcite and dolomite) and minor ones (quartz).The samples display typical EPR spectra of Mn2+ in calcite and reveal the presence of Fe3+ ions.

Electrical conductivity and charge/discharge profiles of mixed polyanion glass-ceramic cathodes for use in Na-ion batteries

Mixed polyanion glass and glass-ceramic cathodes can have the potential to overcome the disadvantages of achieving high theoretical capacities of promising crystalline network. Three targeted cathode compositions were chosen for the present study (NaFe0.5(VO)0.5PO4, NaMn0.7(VO)0.3PO4 and NaCo0.7(VO)0.3PO4) based on the superior performance over their crystalline counter parts with highest current density ~ 100 mAh/g. XRD results displayed that major crystalline phases (Na2FeP2O7 (COD ID: 4001802), Na2MnP2O7 (ICSD ID: 71229)) which are precipitated with an ordered triclinic, P1 structure. However, Na2CoP2O7 (ICSD ID: 71230) crystalline phase exhibits orthorhombic/P n a 21 structure. The highest conducting glass-ceramic cathode sample NaCo0.7(VO)0.3PO4 (σ = 6.41 × 10−7 S·cm−1) retains its discharge capacity retention as 84.5 mAh g−1 (91%) even after 50 cycles. At a high rate of 10C, NaFe0.5(VO)0.5PO4 cathode sample is achieved to be highest discharge capacity retention 69.7% than NaCo0.7(VO)0.3PO4 (53.76%) which is a significant feature of mixed polyanion family of glass-ceramic cathodes.

Crystal structures and photoluminescences of Ce-activated polymer-derived silicon oxynitride phosphors

A series of cerium (Ce)-activated silicon oxynitride samples with various amounts of Ce (x, wt%) was prepared by employing the polymer-derived method with polycarbosilane and Ce acetylacetonate as starting materials. The photoluminescence spectra of the samples were measured. The chemical compositions and states, phase structures, and microstructures of the samples were investigated. It was found that β-Si3N4:Ce phase existed in all the samples, accompanied by α-Si3N4:Ce and CeSi3N5 phases in the samples with x ≤ 6.42, and by CeSiO2N and CeSi3N5 phases in the samples with x > 6.42. All samples showed excitation peaks in the region of 225–400 nm and blue emissions in the range of 420–450 nm. Among them, the sample with x = 6.42 exhibited the strongest blue emission at 445 nm with the excitation at 360 nm, and consisted of both crystalline and amorphous phases. The major crystalline phase β-Si3N4:Ce appeared in two space groups P63 and P63/m, leading Ce ions to be either six or nine coordinated by N/O atoms. The amorphous component contained Si-Si, Si-C, Si-O, and C-C bonds. By analyzing effects of crystalline phase on emission intensity, the difference in contributions of crystalline phases on emission intensity of the samples is discussed.

Crystallization Kinetics and Heat Treatment Temperature on Microstructure of Na<sub>2</sub>O-CaO-P<sub>2</sub>O<sub>5</sub>-TiO<sub>2</sub> Glass System

Bioactive glass ceramics from Na2O-CaO-P2O5-TiO2 system have been fabricated by conventional melt quenching method. In order to change the fabricated glass to glass ceramic samples, a heat treatment technique was employed using temperatures ranging between 700 and 900°C for 2 h. Glass transition and crystallization temperature were analyzed via differential thermal analyzer (DTA). In addition, phase formation and microstructure of the glass-ceramics were also investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). From the crystallization kinetics, the crystallization rate constant (n) of the glass was found to be close to the value of 3, indicating the two-dimensional growth of crystals occurred in the glass ceramics. From the XRD results, the major crystalline phases were sodium titanium phosphate and calcium sodium phosphate along with titanium dioxide as the minor crystalline phases presented in high heat treatment temperatures (750-900°C) of the glass ceramics. SEM of the crystallized base glass Na2O-CaO-P2O5-TiO2 system, showed that crystallization of dendritic-like growths in the glass ceramics.

Effects of Na2O/BaO ratio on the structure and the physical properties of low-temperature glass-ceramic vitrified bonds

Effects of Na2O/BaO ratio on the structure and the physical properties of Li2O-Al2O-B2O3-SiO2 low-temperature glass-ceramic vitrified bonds had been systematically studied. Structure and properties of as-quenched samples were analyzed by DSC, FTIR, and Raman. According to the results of (X3)2/X2 derived from deconvolution results of Raman, the degree of polymerization (DOP) of glass structure decreased with increasing Na2O/BaO. In addition, LiAlSi2O6 and LiAlSi3O8 were the major crystalline phases in the vitrified bonds sintered at 730 °C for 2 h. Meanwhile, Li2SiO3 and BaAl2Si2O8 were determined as the minor crystalline phases by XRD. The results showed that the addition of Na2O promoted the coefficient of thermal expansion (CTE) of vitrified bonds sintered at 730 °C for 2 h. Bending strength tests and SEM indicated that the optimum content of dispersed plate-like BaAl2Si2O8 crystals inlaid in A2 (Na2O/BaO = 0.33) vitrified bonds contributed to showing the highest mechanical strength among the five samples. Moreover, SEM and EDS proved the wettability between A2 vitrified bonds and cBN grains were effective.

Fe nanoparticles produced by electric explosion of wire for new generation of magneto-rheological fluids

Iron magnetic nanoparticles were produced by the technique of the electric explosion of a wire (EEW). The major crystalline phase (95 ± 1%) was α-Fe with lattice parameter a = 0.2863(3) nm. The size of the coherent diffraction domains of this phase was 77 ± 3 nm. The EEW MNPs presented a large saturation magnetization value, reaching about 87% of the saturation magnetization of the bulk iron. EEW NMPs demonstrated an improved magnetic performance when used in magnetorheological (MR) fluids with respect to the commercial carbonyl iron particles (CIPs) micron-sized particles studied for comparison. The MR fluids composed with the EEW nanoparticles showed larger yield stress values than those with CIP micron-sized particles, so proving that the EEW MNPs have a high potential for MR fluids applications.

Risk assessment of bottom ash from fuel oil power plant of Italy: mineralogical, chemical and leaching characterization

The main aim of the present study is to contribute to the field of environmental research by providing new data on bottom ash samples derived from an oil power plant located in Southern Italy. To achieve this purpose, the mineralogical and chemical properties of representative bottom ash samples were investigated through the integrated employment of different analytical techniques, i.e., X-ray powder diffraction, scanning electron microscopy, X-ray fluorescence and atomic absorption spectrometry. The obtained experimental results show that quartz, alunogen, rhomboclase and potassium hydrogen silicate are the major crystalline phases of all the analyzed samples. Furthermore, the revealed main ash constituents are SiO2 and SO3, with low contents of Fe2O3 and Al2O3, and little amounts of CaO, Na2O, K2O, MgO, P2O5 and TiO2. Among the trace elements, very high amounts of heavy metals, i.e., V, Cr, Ni, La, Pb and Mo, were detected. The comparison of the obtained heavy metal abundance data with those reported in the literature highlights significant differences. Leaching test evidenced V, Ni and Cr values that make these ashes a potential contamination source for groundwater quality and for soil, nearby the ash disposal landfills area. All the obtained findings show that these materials are highly harmful for the human health, with a greater extent for the heavy metal concentrations.

Preparation and Structural Characterization of Free-Standing Octacalcium-Phosphate-Rich Thin Films.

Free-standing films of calcium phosphates exhibit many favorable properties for tissue engineering. In this work, a thin film of calcium phosphate is prepared in a liposome suspension using the method of ammonia gas diffusion. The thickness of the film is about 10 μm, and the lateral dimensions are on the length scale of millimeter. The results of powder X-ray diffraction and transmission electron microscopy show that the thin films contain the mineral phases of hydroxyapatite and octacalcium phosphate (OCP). Using solid-state NMR spectroscopy, in particular the technique of heteronuclear correlation spectroscopy with variable contact time, the major crystalline phase of the thin film has been confirmed to be OCP.

Photocatalytic evaluation of the magnetic core@shell system (Co,Mn)Fe2O4@TiO2 obtained by the modified Pechini method

TiO2 is a highly active photocatalyst, sometimes obtained with nanometric particle size, which improves its behavior but makes its removal from aqueous media more difficult. To avoid this drawback, this work aims to obtain a photocatalyst easily removable from aqueous media using magnetism. The core@shell system (Co,Mn)Fe2O4@TiO2 was prepared by adding commercial (Co,Mn)Fe2O4 nanoparticles to the titanium polymeric resin synthesized by the modified Pechini method. Optimization of photocatalyst properties was achieved by variation of the TiO2:ferrite ratio, synthesis temperature and time, followed by their evaluation in photodegradation of an azo dye. The highest efficiency was attained when anatase was the major crystalline phase, whereas TiO2:ferrite ratio was limited to 90% to retain the magnetic properties, which enabled its removal from aqueous media using simple magnets. The system (Co,Mn)Fe2O4@TiO2, synthesized with 90% TiO2 and calcined at 500 °C for 8 h, presented a discoloration of 76.3% after 16 h of exposure to UV light.

Change in re-use value of incinerated sewage sludge ash due to chemical extraction of phosphorus

The potential of six different extractants to recover phosphorus (P) from incinerated sewage sludge ash (ISSA) was evaluated. Secondary effects such as the co-dissolution of Zn and Cu were also considered. The residual ISSA from each study was assessed in particular detail, focusing on the leachability of remaining Zn and Cu, major element composition, crystalline phases and overall degree of crystallinity and particle size distribution. The residual ISSA was also evaluated as a pozzolanic material using a Strength Activity Index (SAI) test with mortars containing Portland cement with a 20% substitution by ISSA. All results were compared to tests with untreated ISSA. Overall, the use of 3 of the 6 extractants could be ruled out due to poor P recovery potential and/or a serious compromise of the potential reuse of residual ISSA in Portland cement-based materials. The results highlight the added value of considering the potential reuse of residual ISSA when trying to optimize P recovery from ISSA by wet methods.

Investigation of Methylammonium Tin Strontium Bromide Perovskite Systems

The properties of methylammonium-tin-strontium bromide systems (CH3NH3Sn1-xSrxBr3, 0.0 ≤ x ≤ 0.1) were investigated. The X-ray diffraction analysis (XRD) revealed the presence of the untilted cubic Pm-3m perovskite and orthorhombic SnBr2 as major crystalline phases. The morphological analysis confirmed the XRD data by detecting the formation of polyhedral shaped crystallites attributed to MASnBr3 perovskite and elongated crystallites related to SnBr2 phase. Derivative differential thermal analysis (DDTA) and derivative thermogravimetric analysis (DTG) revealed a thermal stability of MASnBr3 phase till T = 250°C and showed the presence of more thermal events related to a multistep decomposition process. The addition of Sr-ions retained the cubic crystalline structure of the perovskite and enhanced its thermal stability at T = 150°C by reducing the weight loss rates. The optical spectra displayed values of absorption edges between 624 nm and 636 nm. The Tauc plots revealed a direct semiconducting behavior with band energy gaps at ∼2.02–2.03 eV. The emission photoluminescence (PL) spectra, measured at room temperature and excitation wavelength λexc = 380 nm as well as the excitation photoluminescence (PL) spectra, measured at room temperature and emission wavelength λem = 520 nm showed a dramatic increase of the intensity by adding the Sr-ions reaching a maximum for x = 0.025.

Crystallization and Dielectric Properties of Transparent Na2O-Nb2O5-SiO2 Based Glass-Ceramics

Na2O-Nb2O5-SiO2 based glass-ceramics with and without ZrO2/TiO2 were prepared by controlled crystallization, and their crystallization properties under different heat-treatment temperatures were characterized by differential scanning calorimetry, X-Ray Diffraction (XRD) and morphology observation. The XRD results indicated the presence of NaNbO3 with perovskite structure as the major crystalline phase. The introduction of ZrO2 contributed to the stabilization of the Na2O-Nb2O5-SiO2 basic glass, and thus improved their crystallization. Moreover, changes of the dielectric constant of the glass-ceramics with the frequency and measuring temperature were mainly studied. In details, the maximum dielectric constant reached 136.9 (@1000 KHz, 25°C), and the rate of change with temperature is as small as about −0.0302/°C. The crystalline glass remains transparent in the range of 400–800 nm, and the transmittance is above 70% for the 2 mm thick sample.

Influence of ZnO and Heat Treatment Process on the Physical and Optical Properties of MgO-Al2O3-SiO2 Glass-Ceramics

The influences of adding ZnO and the use of specific heat-treatment schedules on MgO-Al2O3-SiO2 (MAS) glass-ceramic properties including crystallization, micromorphology, optical transmittance and Vickers-hardness were investigated. The XRD analysis proved that MgAl2O4 and Al2ZnO4 spinel are the major crystalline phases formed in the studied MgO-Al2O3-SiO2-ZnO (MASZ) glass ceramics. The addition of ZnO facilitated the crystallization of the MAS glass and resulted in a uniform and compact microstructure. The homogeneous distribution of microcrystals with average grain size less than 100 nm in the MASZ glass-ceramics contributed to the improvement of the corresponding transmittance in the visible range. In addition, the orthogonal heat-treatment experiment indicated that the crystallization time and nucleation time have a dominant effect on the microhardness of glass-ceramics, followed by decreasing effects of crystallization temperature and nucleation temperature.

Photocatalytic reduction of carbon dioxide over Cu/TiO2 photocatalysts.

The photocatalytic reduction of CO2 with H2O was investigated using Cu/TiO2 photocatalysts in aqueous solution. For this purpose, Cu/TiO2 photocatalysts (with 0.2, 0.9, 2, 4, and 6wt.% of Cu) have been synthesized via sol-gel method. The photocatalysts were extensively characterized by means of inductively coupled plasma optical emission spectrometry (ICP-OES), N2 physisorption (BET), XRD, UV-vis DRS, FT-IR, Raman spectroscopy, TEM-EDX, and photoelectrochemical measurements. The as-prepared photocatalysts contain anatase as a major crystalline phase with a crystallite size around 13nm. By increasing the amount of Cu, specific surface area and band gap energy decreased in addition to the formation of large agglomeration of CuO. Results revealed that the photocatalytic reduction of CO2 decreased in the presence of Cu/TiO2 in comparison to pure TiO2, which might be associated to the formation of CuO phase acting as a recombination center of generated electron-hole pair. Decreasing of photoactivity can also be connected with a very low position of conduction band of photocatalysts with high Cu content, which makes H2 production necessary for CO2 reduction more difficult.

Atmospheric Corrosion of Hot Dip Zinc Coated Steel in Coastal and Rural Areas of Vietnam

The comparative results of corrosion testing in humid tropical atmosphere in rural and coastal areas for hot dipped zinc coatings are presented below. The test was conducted in outdoor conditions over a period of five years. The mass loss and other performance characteristics of two types of zinc coatings were evaluated, analysed and discussed in relation to the climatic and environmental parameters. The corrosion rates of the coatings exposed to coastal conditions were about three times higher than the corrosion rates appreciated in rural conditions. The data demonstrates that the corrosion process obeys an equation of the form M=At n , where M is the loss of metal and t is the time of exposure. A and n are constants which values depend on the environmental characteristics and the physicochemical behavior of the corrosion products respectively. Corrosion is strongly influenced by atmospheric time of wetness (TOW) and airborne salinity. The nature and composition of corrosion products are also considered. Simonkolleite, a major crystalline phase, was found in the zinc corrosion products exposed to coastal conditions, while zinc hydroxide and zinc hydrosulfate are easily found in rural settings.

Thermodynamic effect on interaction between crystalline phases in size-controlled ACC-bacterial nanocellulose and poly(vinyl alcohol)

The aqueous counter collision (ACC) method can provide single bacterial nanocellulose ribbons (ACC-BNC) in a desired width, from a pellicle produced by Gluconacetobacter xylinus. Kose et al. (Biomacromolecules, 12:716–720, 2011) reported that the ACC process transformed the major Iα crystalline phase of the native fiber to a stable Iβ phase, without decreasing the overall crystallinity. The current study investigated the variation of the crystalline phases of ACC-BNC, upon interaction with poly(vinyl alcohol) (PVA). ACC-BNC of desired width was mixed with PVA, without any chemical reaction occurring. This resulted in a homogeneous suspension. The equilibrium melting point of PVA in cast nanocomposite films was investigated, as a probe for evaluating the crystalline surface properties of the ACC-BNC. A decrease in the equilibrium melting point of PVA would have indicated attractive interactions between the PVA and ACC-BNC. However, the nature of the ACC-BNC surface in the presence of PVA depended on the ACC-BNC width. Thicker ACC-BNC acted as a nucleating agent for PVA. Thinner ACC-BNC acted as a diluent of PVA. This tendency was opposite to the case for Iβ-dominant ACC-wood nanocellulose. ACC-BNC acting as a nucleating agent was more efficient than ACC-wood nanocellulose. The results suggested that ACC-BNC surfaces, which probably contained I α phases, had different characteristics to those of Iβ-dominant ACC-wood nanocellulose surfaces.

Utilization of reduction slag and waste sludge for Portland cement clinker production

The feasibility of recycling the reduction slag, limestone sludge, iron‐oxide sludge, and stone sludge produced in the manufacture of cement was investigated through compressive strength testing, differential thermal and thermogravimetric analysis, X‐ray diffraction, and 29Si nuclear magnetic resonance analysis. The major crystalline phases of ecocement clinkers, namely C3S, β‐C2S, C4AF, and C3A, were observed. C3S content decreased and β‐C2S and α‐C2S content increased in the reduction slag. The compressive strength of EcoA pastes (ecocement contain 78% of limestone sludge, 19.51% of stone sludge and 2.49% iron‐oxide sludge) was similar to that of commercial ordinary Portland cement. The Q0 (−70 ppm) species shifted to the Q1 (−80 ppm), and Q2 (−87 ppm) species during curing. The addition of stone sludge, iron‐oxide sludge, and limestone sludge had no negative effect on the hydration of the cement pastes. In contrast, the addition of reduction slag negatively affected the formation of clinker minerals. Cement samples with reduction slag content of 1–7 wt % had lower 28‐, 60‐, and 90‐day compressive strength than did the control mix. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 669–677, 2018