Crystalline Phase Composition Research Articles

Influences of Processing Time and Discharge Current Density During Pulsed Plasma-Oxidizing process of AISI 316L

The influences of discharge current density and oxidation process duration on surface morphology, crystalline phase composition, and electrochemical corrosion performance of pulsed plasma-oxidized AISI 316L stainless steel were studied. Analysis of results shows that samples treated through DC pulsed plasma oxidation (0.5 mA/cm2, 60 min) exhibit corrosion current values of 2.0 × 10−4 mA/cm2 which represent one eighth of the corrosion current obtained for untreated samples and one half that of chemically passivated samples. Scanning electron microscopy, grazing incidence x-ray diffraction, and Raman analysis show that the improved corrosion performance of oxidized samples could be attributed to morphological changes of the oxidized layer which is composed of hematite and magnetite iron oxides. Corrosion performances of DC plasma-oxidized samples suggest that through this technique, it is possible to obtain comparable or even better corrosion performance than techniques, such as inductively coupled plasma-oxidizing process, but without the inherent higher instrumental requirements of radiofrequency plasma processes.

The effect of reaction conditions on formation of wet precipitated calcium phosphates

The precipitation process discussed in the present study involves the addition of alkaline solutions to an acidic calcium phosphate suspension. Several parameters (pH, pH buffer reagent, ageing and stirring) were investigated. The synthesized powders were calcined at 1000°C for 1 h in air, in order to study the thermal stability and crystalline phase compositions. X-ray diffraction (XRD) and ESEM analysis were used for sample characterization. It is found that all these processing parameters affect the crystalline phases evolved and resultant microstructures. Phase evolution occurred at an elevated pH level. The pH buffer reagent would affect both the phase composition and microstructure. Ageing was essential for the phase maturation. Stirring accelerated the reaction process by providing a homogeneous medium for precipitation.

Surfactant-assisted hydrothermal synthesis of Fluoridated Hydroxyapatite nanorods

Fluoridated Hydroxyapatite (FHA) nanorods were synthesized using Apricot Tree Gum (ATG) as a novel surfactant and then compared with Ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) and Sodium Dodecyl Sulfate (SDS) as conventional surfactant agents under hydrothermal condition (70°C and 1atm). The effects of pH values and various types of surfactants on the formation of the FHA nanorods, crystalline phase, and chemical compositions were investigated using Field Emission Scanning Electron Microscopy (FESEM) equipped by Energy Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The findings indicated application of the presented ATG as surfactant is able to produce the hexagonal nanorods of FHA along their c-axis direction. Moreover, it is illustrated that diameter and length of nanorods which is obtained by ATG surfactant are bigger than EDTA and SDS. In addition, it is demonstrated that pH values can play a major role on formation of hexagonal FHA nanorods. The increase of pH transformed the shape of synthesized FHA from particles to rods. Ultimately, based on the similarity of synthesized FHA nanorods to the shape, structure, and composition of enamel; it is suggested for its potential to be used for dental applications.

Phase control of iron oxides grown in nano-scale structures on FTO and Si(100): Hematite, maghemite and magnetite

We demonstrate that iron oxide in the form of hematite, suitable as absorption material in photoelectrochemical cells, can be produced by pulsed chemical vapour deposition. By choosing carbon monoxide or nitrogen as carrier gases in the process the phase and granularity of the grown material can be controlled. The choice of carrier gas affect the decomposition rate of iron pentacarbonyl used as iron precursor. The iron oxide phase is also dependent on the chosen substrate, here fluorine doped tin oxide and crystalline silicon have been used. Regardless of the substrate nitrogen yields hematite, whereas carbon monoxide gives magnetite on Si and maghemite on fluorine doped tin oxide. A combination of Raman spectroscopy, X-ray diffraction, and hard X-ray photoelectron spectroscopy were used for characterization of the crystalline phase and chemical composition in the films. Scanning electron microscopy were used to visualise the deposited films' nano-structure.

Carbothermic reactions of mechanically milled coal and wolframite mixtures under Ar and N2 atmospheres

The thermal reactions of mechanically activated coal and natural wolframite mixtures have been studied using DTA–TG. The reaction mixture, prepared on the basis of a thermodynamic simulation, was milled in a planetary ball mill for either 2 or 4 h. Unmilled and milled mixtures were subjected to differential thermal analysis under nitrogen and argon atmospheres with the crystalline phase composition determined with XRD. The main differences between nitrogen and argon atmospheres were observed in the raw samples. Milled samples produced primarily an iron tungsten phase, Fe7W6. Under the nitrogen atmosphere, both samples showed a greater extent of reduction than under argon.

Development of a sintering process for recycling oil shale fly ash and municipal solid waste incineration bottom ash into glass ceramic composite

Oil shale fly ash and municipal solid waste incineration bottom ash are industrial and municipal by-products that require further treatment before disposal to avoid polluting the environment. In the study, they were mixed and vitrified into the slag by the melt-quench process. The obtained vitrified slag was then mixed with various percentages of oil shale fly ash and converted into glass ceramic composites by the subsequent sintering process. Differential thermal analysis was used to study the thermal characteristics and determine the sintering temperatures. X-ray diffraction analysis was used to analyze the crystalline phase compositions. Sintering shrinkage, weight loss on ignition, density and compressive strength were tested to determine the optimum preparation condition and study the co-sintering mechanism of vitrified amorphous slag and oil shale fly ash. The results showed the product performances increased with the increase of sintering temperatures and the proportion of vitrified slag to oil shale fly ash. Glass ceramic composite (vitrified slag content of 80%, oil shale fly ash content of 20%, sintering temperature of 1000°C and sintering time of 2h) showed the properties of density of 1.92±0.05g/cm3, weight loss on ignition of 6.14±0.18%, sintering shrinkage of 22.06±0.6% and compressive strength of 67±14MPa. The results indicated that it was a comparable waste-based material compared to previous researches. In particular, the energy consumption in the production process was reduced compared to conventional vitrification and sintering method. Chemical resistance and heavy metals leaching results of glass ceramic composites further confirmed the possibility of its engineering applications.

Nanosized titanium dioxide reduces copper toxicity--the role of organic material and the crystalline phase.

Titanium dioxide nanoparticles (nTiO2) are expected to interact with natural substances and other chemicals in the environment, however little is known about their combined effects. Therefore, this study assessed the toxicity of copper (Cu) in combination with varying crystalline phases (anatase, rutile, and the mixture) of nTiO2 and differing organic materials on Daphnia magna. The nanoparticles reduced the Cu-toxicity depending on the product (0.3- to 2-fold higher 48-h EC50). This decrease in toxicity coincided with a lowered Cu-concentration in the water column, which was driven by the adsorption of Cu to nTiO2-depending on available surface area and structure-and their subsequent sedimentation. In the presence of organic material and nTiO2, the Cu-toxicity was further reduced (up to 7-fold higher 48-h EC50). This observation can be explained by a reduced Cu-bioavailability as a result of complexation and adsorption by the organic material and nTiO2, respectively. Thus, the crystalline phase composition, which is determining the surface area and structure of nTiO2, seems to be of major importance for the toxicity reduction of heavy metals, while the influence of the organic materials was mainly driven by the quantity and quality of humic substances.

The effect of mechanical milling on the soft magnetic properties of amorphous FINEMET alloy

The effect of milling time on the magnetic properties of FINEMET amorphous ribbons has been investigated using X-ray diffraction, Mössbauer spectroscopy, thermo-magnetic measurements, transmission electron microscopy and SQUID magnetometery. Ribbons were melt-spun at a wheel speed of 38 ms-1 and then mechanically milled for different periods up to 45 min. The results showed that the partially crystallization of the amorphous powder occurs during milling. TEM observations confirmed the formation of small volume fraction of the crystalline phase with ~9 nm crystallite size in the amorphous matrix for the ribbon milled for 45 min. Thermo-magnetic measurements indicated the enhancement of the Curie temperature of amorphous phase during milling which is due to the annihilation of free volumes and microstructural ordering. The Hopkinson effect led to the monotonic increase of magnetization with respect to the temperature before reaching the Curie temperature of the milled samples. Moreover; the magnetization increased with the formation of the Fe(Si) phase while the coercivity decreased. Mössbauer spectroscopy and thermo-magnetic measurements revealed the existence of 13% Fe in crystalline phase. The composition of crystalline phase was determined as Fe–16.5Si. Hyperfine field values increased with milling time, suggesting the ordering of the structure and enhancement of the number of Fe–Fe atomic pairs in the crystalline phase comparing to the primary amorphous ribbon.

The recycling of incinerated sewage sludge ash as a raw material for CaO–Al2O3–SiO2–P2O5 glass-ceramic production

In this paper, the recycling of incinerated sewage sludge ash (ISSA) into glass-ceramic materials by a two-stage sintering cycle of nucleation stage and crystallization stage without any pressure and binder is presented. The parent glasses were subjected to the following nucleation/crystallization temperature and time level: (A) 790°C, 1.0 h/870°C, 1.0–3.0 h; (B) 790°C, 1.0 h/945°C, 1.0–3.0 h and (C) 790°C, 1.0 h/1065°C, 1.0–3.0 h. X-ray power diffraction analysis results revealed that multiple crystalline phases coexisted in the glass-ceramic materials and the crystalline phase compositions were more affected by crystallization temperature than crystallization time. Scanning electron microscopy analysis showed an interlocking microstructure of glass phases and crystals with different sizes and spatial distribution. The glass-ceramics crystallized at 945°C for 2.0 h exhibited optimal properties of density of 2.88 ± 0.08 g/cm3, compression strength of 247 ± 12 MPa, bending strength of 118 ± 14 MPa and water absorption of 0.42 ± 0.04. The leaching concentrations of heavy metals were far lower than the limits required by the regulatory standard of EPA. This paper provides a feasible, low-cost and promising method to produce ISSA-based glass-ceramics and highlights the principal characteristics that must be taken into account to use ISSA correctly in glass-ceramics.

Crystallization kinetics of calcium–magnesium aluminosilicate (CMAS) glass

The crystallization kinetics of a calcium–magnesium aluminosilicate (CMAS) glass with composition relevant for aerospace applications, like air-breathing engines, were evaluated using differential thermal analysis (DTA) in powder and bulk forms. Activation energy and frequency factor values for crystallization of the glass were evaluated. X-ray diffraction (XRD) was used to investigate the onset of crystallization and the phases that developed after heat treating bulk glass at temperatures ranging from 690°C to 960°C for various times. Samples annealed at temperatures below 900°C remained amorphous, while specimens heat treated at and above 900°C exhibited crystallinity originating at the surface. The crystalline phases were identified as wollastonite (CaSiO3) and aluminum diopside (Ca(Mg,Al)(Si,Al)2O6). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were employed to examine the microstructure and chemical compositions of crystalline phases formed after heat treatment.

Liquid and Solid Compound Granulated Diurea Sulfate-Based Fertilizers for Sustainable Sulfur Source

Design and manufacture of high nitrogen content sulfur-containing fertilizers is of crucial importance in sustainable food and energy crop production. The availability of large elemental sulfur amounts in oil refining and natural gas processing facilities, in combination with decreasing sulfur deposition into soil from natural and anthropogenic sources in a bioavailable sulfate form, calls for innovative engineering solutions that bridge this gap via sustainable sulfur processing. Diurea sulfate-based liquid and compound solid granulated fertilizers were synthesized in this work, and their resulting physicochemical properties were determined. First, phase compositional information on the 2CO(NH2)2·H2SO4–CO(NH2)2–H2O ternary system was measured, and high nitrogen content, ∼15:1 N:S ratio liquid fertilizer grades, were established. Next, diurea sulfate granulation experiments using (i) dolomite, (ii) byproduct material after the phosphoric acid extractive production, CaSO4·0.5H2O, and (iii) dolomite combined with diammonium phosphate, (NH4)2HPO4, and potassium chloride, KCl, were performed. Using diurea sulfate, 16–16–16–5.5(S)–0.4(MgO)–0.6(CaO) compound granulated fertilizers were successfully obtained, and time-resolved changes in their crystalline phase composition during granule curing were monitored using XRD. The granule crushing strength measured increased to 3.800 MPa within the 30 day storage thus resulting in high quality fertilizer material.

Crystallization and microstructure of CaO–MgO–Al2O3–SiO2 glass–ceramics containing complex nucleation agents

The CaO–MgO–Al2O3–SiO2 (CMAS) glass–ceramics containing binary complex nucleation agents were prepared by body crystallization process, and the effects of complex nucleation agents on the crystallization and microstructure of CMAS glass–ceramics were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The complex nucleation agents consist of constant fluorine (8.0wt.% CaF2) and different oxides (3.0wt.% TiO2, ZrO2, or P2O5). Compared with the CMAS glass with only CaF2, the respective addition of oxides promotes the crystallization of CMAS glass, especially TiO2 or P2O5. The addition of TiO2 or ZrO2 has no obvious effect on the compositions of main crystalline phases, while P2O5 results in the precipitation of pyroxene phase instead of diopside phase, with the existence of more small crystals. The CMAS glass–ceramic containing CaF2+TiO2 or CaF2+P2O5 achieves full body crystallization with high crystallization ratio, and has high hardness, good chemical resistance and water absorption.

Preparation and photocatalytic properties of core-shell nano-TiO2 @ α-Al2O3 microspheres.

Core-shell nano-TiO2@a-Al2O3 microspheres of 5-20 μm were prepared by the heterogeneous precipitation method combined with the hydro-thermal and calcination process using α-Al2O3 microspheres as substrate. Their morphologies, microstructure and crystalline phase were characterized by SEM and XRD respectively. The photocatalytic activity was evaluated by degradation of methyl orange. The as-prepared 10 wt.% nano-TiO2@α -Al2O3 microspheres possess α core-shell structure with a monolayer of nano-TiO2 particles less than 30 nm on the surface of α-Al2O3 microspheres. Their photocatalytic properties are largely influenced by the calcination temperature and the sample calcined at 800 degrees C for 2 h has the best photocatalytic activity. This high photocatalytic activity can be attributed to the synergetic effects of the unique structure of nano-TiO2 @α-Al2O3 microspheres, quantum size effect, composition of crystalline phase and crystallinity of nano-TiO2. These nano-TiO2@α-Al2O3 microspheres may be conveniently separable and useful in practical treatment of organic waste waters due to the large particle size and high photocatalytic properties.

Influence of Synthesis Parameters on the Formation of SAPO-5 from Metakaolin

SAPO-5 molecular sieves was hydrothermally synthesized using metakaolin simultaneously as silica and aluminum sources, triethylamine as template agent, and phosphoric acid as phosphorous source. The influence of crystallization time, amount of triethylamine, hydrofluoric acid, and water on the structure and composition of crystalline phase were investigated. The structure and composition of product were analyzed by means of XRD, and BET. It was showed that the SAPO-5 molecular sieves with high crystallinity and well-defined morphology can be synthesized with a molar ratio of MK:P2O5:2.5TEA: 0.1HF:70H2O in the final reaction mixture at 200°C for 24h.

Brookite TiO2-based materials: Synthesis and photocatalytic performance in oxidation of methyl orange and As(III) in aqueous suspensions

A series of titania samples consisting of pure brookite, brookite/anatase and brookite/layered titanate hybrids were synthesized by a hydrothermal method. The influence of experimental variables, including electrolyte concentration, temperature and duration of hydrothermal treatment, on structural and physical properties of the resulting materials was investigated. The crystalline phase composition of the materials was analyzed by X-ray diffraction, the morphology was examined by scanning electron microscopy (SEM) and the specific surface areas were measured according to the Brunauer–Emmett–Teller method. Pure brookite could be obtained by hydrothermal treatment at 180°C with addition of 0.25M NaCl, 0.5M NaCl or 0.1M NaOH, and adjustment of reaction time. Brookite samples prepared by addition of NaCl as source of Na+ ions showed a flower-type morphology, whereas those synthesized with NaOH consisted in micrometric-size aggregations of nanoparticles. The photocatalytic activity of the materials was evaluated by means of methyl orange bleaching and by As(III) to As(V) oxidation.

Effect of solute atoms on glass-forming ability for Fe–Y–B alloy: An ab initio molecular dynamics study

The glass-forming abilities of Fe78B22, Fe70Y6B24, Fe72Y6B22 and Fe72.5Y3.5B24 alloys were characterized comprehensively using ab initio molecular dynamics simulations. The calculated results were correlated with the properties and atomic structures. It was found that the Fe72Y6B22 alloy consists of both the most stable and the least deformed body centered cubic atomic packing structures in the supercooled liquid and glassy states. It was observed that the local compositions in the Fe72Y6B22 alloy significantly deviate from the compositions of stable crystalline phases, indicating that the Fe72Y6B22 alloy has the best glass-forming ability among the alloys studied. However, Fe72Y6B22 alloy has two flaws in terms of glass-forming ability, i.e. relatively large atomic diffusivity and insufficiently close atomic packing. The best performance in these two aspects is observed in the Fe72.5Y3.5B24 alloy. Thus, the theoretical study predicts that the best glass former for the Fe–Y–B system is within the compositional range of 22–24at.% B and 3.5–6at.% Y.

Structure of Na2O–MgO–CaO–SiO2 glasses by combined Raman spectroscopy and thermodynamic modeling approach

The present contribution deals with the Raman spectra and structure of Na2O–MgO–CaO–SiO2 glasses. Six glasses with the trisilicate overall composition 15Na2O·xMgO·(10–x)CaO·75SiO2 (x = 0, 2, 4, 6, 8, 10) were studied. The structure of studied glasses was described by the thermodynamic model of Shakhmatkin and Vedishcheva. From the 27 components with the stoichiometry given by the composition of stable crystalline phases, only eight were found in significant abundance in the studied glasses—namely: SiO2, 2MgO·SiO2 (M2S), MgO·SiO2 (MS), Na2O·3CaO·6SiO2 (NC3S6), Na2O·CaO·5SiO2 (NCS5), Na2O·MgO·4SiO2 (NMS4), Na2O·SiO2 (NS), and Na2O·2SiO2 (NS2). The correlation analysis points out that the strong positive correlations between the equilibrium molar amounts of: {M2S–MS–SiO2}, {NC3S6–NCS5}, and {NMS4–NS–NS2}. From the components of significant abundance, only the content of MS and NC3S6 change significantly within the studied compositional series. These two components were identified with the result of the principal component analysis of Raman spectra that indicated the presence of two independent spectral components. Using the method of Malfait the partial Raman spectra of MS and NC3S6 components were found. The obtained results very well reproduce the experimental Raman spectra and confirmed in such way the thermodynamic model.

Bimetallic Gold-Palladium Supported on 5A Zeolite and their Catalytic Activity for Vinyl Acetate Synthesis

5A zeolite supported Gold-Palladium (Au-Pd) bimetallic were prepared and used in vapor phase oxidation of ethylene to synthetize vinyl acetate (VA). The chemical composition of Au-Pd/5A zeolite catalyst was analyzed by a combination of atomic absorption spectrometry (AAS). The structure of Au-Pd/5A zeolite catalyst was characterized by a scanning electron microscopy (SEM) and X-ray diffraction (XRD). The catalytic activity of the Au-Pd/5A zeolite catalyst under laboratory conditions were investigated in vinyl acetate synthesis by a kind of the fixed bed reaction device. The AAS testing showed that Au and Pd supported rate were increased up to the optimum value 91.22% and 93.91% respectively at the ratio of Au/Pd=0.87. The SEM analysis results indicated that Au-Pd alloy particles of 5A zeolite catalyst can grown up and reunited obviously through before and after reaction. The XRD analysis results showed that diffraction peak of Pd (111), Pd (200), Au (111) and Au (200) became sharp gradually with the extension of reaction time, crystalline phase composition and grain size of catalyst became bigger gradually. The results about catalytic activity of the Au-Pd/5A zeolite catalyst shown that with the increasing of the Au/Pd ratio, the space-time yield and selectivity have a best value respectively; when the ratio of Au/Pd=0.87, the space-time yield were 702g/(Lh) and the selectivity were 92.8% at the ratio of Au/Pd =1.13.

Electrophoretic deposition of bioactive glass nanopowders on magnesium based alloy for biomedical applications

To slow down the initial biodegradation rate of magnesium (Mg) alloy, crystalline nano-sized bioactive glass coating was used to deposit on micro-arc oxidized AZ91 samples via electrophoretic deposition (EPD). Zeta potential and conductivity of the bioactive glass suspension were characterized at various pH values to identify the most stable dispersion conditions. The bone-bonding properties of bioactive glass coated samples were evaluated in terms of apatite-forming ability during the immersion in simulated body fluid (SBF) solution. Results revealed that the ability to form a bioactive glass coating via EPD was influenced by the degree of its crystalline phase composition. Moreover, the potentiodynamic polarization tests recorded significant drops in corrosion current density and corrosion rate of the coated samples which implies a good level of corrosion protective behavior. These preliminary results show that this process will enable the development of Mg implants in the later stage of bone healing.

Oxygen-sensing properties of electrospun CNTs/PVAc/TiO2 composites

Multi-walled-carbon-nanotubes/polyvinylacetate/titanium oxide (MWCNTs/PVAc/TiO2) composite fibers with different MWCNT loadings were prepared using the electrospinning technique. The addition of cetyl trimethyl ammonium bromide (CTAB) as a surfactant agent to promote the dispersion of the MWCNTs was also evaluated. The morphological and microstructural properties of as-spun and annealed samples in air at 600°C were examined using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and x-ray diffraction (XRD). The sensing characteristics of the synthesized TiO2-based nanostructures were evaluated for oxygen monitoring at moderate temperatures. The effects of the MWCNT loading, the addition of the surfactant and the composition of the TiO2 crystalline phases were investigated and discussed.