Effect Of Crystalline Phase Research Articles

Competition between surficial and volumetric diffusion in sintering TiO2 polymorphs by molecular dynamics simulation

AbstractThe competition between surficial and volumetric diffusion during the sintering process for ceramic polymorphism at different sintering temperatures is worth deeply exploring. In the current work, various sintering cases of mixed TiO2 nanoparticles with rutile and anatase types were investigated and the effects of crystalline phase, sintering temperature, and particle size on the sintering process were systematically investigated. The difference in thermodynamic stability and surficial activity of the crystalline phase could promote the decomposition and densification of the nanoparticles. Comparing the mixed‐phase sintering process at different sintering temperatures, the results showed that the particle binding process at low temperature relied mainly on surficial diffusion, however, volumetric diffusion played a crucial role at high temperature. The internal occurrence of volumetric diffusion inhibited the surficial diffusion, resulting in a smaller diameter of the sintering neck and a different sintering rate. In the case of sintering three nanoparticles with rutile and anatase types, it could be found that the decomposition of nanoparticles is more uniform in mixed‐phase sintering at high temperatures and the sintering rate is not significantly influenced by the sintering temperature. This work demonstrates the advantage of a mixed‐phase sintering strategy for TiO2 nanoparticles, which could provide insight into ceramic materials with polymorphism.

Effect of Crystalline Phase and Facet Nature on the Adsorption of Phosphate Species onto TiO2 Nanoparticles.

The current use of TiO2 nanoparticles raises questions about their impact on our health. Cells interact with these nanoparticles via the phospholipid membrane and, in particular, the phosphate head. This highlights the significance of understanding the interaction between phosphates and nanoparticles possessing distinct crystalline structures, specifically anatase and rutile. It is crucial to determine whether this adsorption varies based on the exposed facet(s). Consequently, various nanoparticles of anatase and rutile TiO2, characterized by well-defined morphologies, were synthesized. In the case of the anatase samples, bipyramids, needles, and cubes were obtained. For the rutile samples, all exhibited a needle-like shape, featuring {110} facets along the long direction of the needles and facets {111} on the upper and lower parts. Phosphate adsorption experiments carried out at pH 2 revealed that the maximum adsorption was relatively consistent across all samples, averaging around 1.5 phosphate·nm-2 in all cases. Experiments using infrared spectroscopy on dried TiO2 powders showed that phosphates were chemisorbed on the surfaces and that the mode of adsorption depended on the crystalline phase and the nature of the facet: the anatase phase favors bidentate adsorption more than the rutile crystalline phase.

Effect of crystalline phase on deformation behaviors of amorphous matrix in a metallic glass composite

In metallic glass composites (MGCs), the existence of crystalline phases causes the structures of amorphous matrix to become relatively heterogeneous near the crystalline phase, resulting in the difference of mechanical properties in micro- or nano-scale in amorphous matrix near crystalline/matrix interface. In this study, this difference was characterized by nanoindentation technology, and the pile-up height was quantitatively related to the activation volume of shear transformation zones (STZs). Molecular dynamics simulations were conducted to investigate the activation behaviors of STZs during nanoindentation process of amorphous matrix. The influences of crystalline phase on deformation behaviors of amorphous matrix near the interface in MGCs were analyzed in details.

Excellent work-hardening in ZrCu/NiNb amorphous/amorphous nanolaminates

Work-hardening behavior could be rarely observed in amorphous alloys during plastic deformation because the dilation and softening effect often occur in shear bands. Here, we proposed a novel mechanism to realize an excellent work-hardening rate (R=dσdε) in ZrCu/NiNb amorphous/amorphous nanolaminates (A/ANLs), which is investigated by in-situ uniaxial micro-pillar compression tests. The work-hardening rate value (25.24 GPa) obtained in ZrCu/NiNb A/ANLs with single layer thickness (h) 5 nm and volume ration 1:1, is relatively high, when comparing with the values in other results that considered the effect of crystalline phases and structural heterogeneity on work-hardening rate in composites. Such a high work-hardening effect is attributed to serious suppression of shear transformation zones (STZs) percolation by amorphous/amorphous interfaces. This work-hardening effect increased sharply as h decreases to 5 nm.

Viscosity of CaO-MgO-Al2O3-SiO2-TiO2-FeO slag with varying TiO2 content: The Effect of Crystallization on Viscosity Abrupt Behavior

Reasonable slag fluidity is essential for stable HIsmelt process operation. During the slag-tapping process, crystallization will cause the slag viscosity to rise sharply, which is not conducive to stable slag-tapping operation, especially for smelting high-titanium slag. In this paper, the viscosity of the CaO-MgO-Al2O3-SiO2-TiO2-FeO slag with varying 10–50% TiO2 content was studied in the laboratory. The crystalline phases of water quenched slag samples at different temperatures were determined by XRD, and it was verified with the results of Factsage thermodynamic calculations. In addition, the effects of crystalline phase, crystalline morphology and crystal size on the critical viscosity of slag were discussed through SEM-EDS analysis. The results show that the proper TiO2 content in the slag is below 40%, the temperature of critical viscosity (Tcv) of the slag is between 1336 °C and 1360 °C, and the Tcv of the slag with a TiO2 content of 50% increases to 1500 °C. The sudden increase in viscosity is related to the crystallization behavior of the slag. With the increase of TiO2 content, the main precipitated titanium-rich phase in the slag changed from dendritic perovskite to plate-shaped pseudobrookite. Among them, when the TiO2 content is 10%, the sharp increase in viscosity of the slag is mainly determined by the precipitation amount of melilite. The amount of crystals in the slag between 20% and 43% causes the viscosity of the slag to rise rapidly, which is mainly due to the fact that the granular crystals have a greater influence on the viscosity than the plate crystals. Compared with the experimental results, it is found that Factsage software cannot accurately calculate the phase equilibrium of slag with a TiO2 content of 40–50%.

Catalytic oxidation of sulfachloropyridazine by MnO2: Effects of crystalline phase and peroxide oxidants

Catalytic activation of different oxidants including peroxymonosulfate (PMS), peroxydisulfate (PDS), hydrogen peroxide (H2O2) and ozone (O3) by MnO2 for degradation of sulfachloropyridazine (SCP) was investigated and the effects of different crystalline phases of MnO2 including nanowire α-MnO2, nanorod β-MnO2, nanofiber γ-MnO2, and nanosphere δ-MnO2 on catalytic ozonation of SCP were also studied. The SCP degradation and total organic carbon removal indicated that the oxidation efficiency of the peroxide oxidants followed an order of O3/MnO2 > PMS/MnO2 > PDS/MnO2 > H2O2/MnO2. In catalytic ozonation, SCP degradation rate constants of different MnO2 phases followed an order of δ-MnO2 > α-MnO2 > γ-MnO2> β-MnO2. Electron paramagnetic resonance (EPR) suggested that hydroxyl radicals (·OH) and singlet oxygen (1O2) might be more significant for SCP degradation than sulfate (SO4·−) and superoxide (·O2−) radicals. Radical competition experiments demonstrated that 1O2 and ·OH contributed to 63.16% and 28.07%, respectively, for the catalytic ozonation of SCP. It was also found that more oxygen vacancies, specific surface area and exposure of MnO6 edges could facilitate the activation of O3 for 1O2 and ·OH productions and SCP degradation. The degradation pathways of SCP could mainly follow the cleavage of S–C or S–N bond and dechlorination, accompanied by hydroxylation and oxidation.

Hydroxyapatite-modified micro/nanostructured titania surfaces with different crystalline phases for osteoblast regulation

Surface structures and physicochemical properties critically influence osseointegration of titanium (Ti) implants. Previous studies have shown that the surface with both micro- and nanoscale roughness may provide multiple features comparable to cell dimensions and thus efficiently regulate cell-material interaction. However, less attention has been made to further optimize the physicochemical properties (e.g., crystalline phase) and to further improve the bioactivity of micro/nanostructured surfaces. Herein, micro/nanostructured titania surfaces with different crystalline phases (amorphous, anatase and anatase/rutile) were prepared and hydroxyapatite (HA) nanorods were deposited onto the as-prepared surfaces by a spin-assisted layer-by-layer assembly method without greatly altering the initial multi-scale morphology and wettability. The effects of crystalline phase, chemical composition and wettability on osteoblast response were investigated. It is noted that all the micro/nanostructured surfaces with/without HA modification presented superamphiphilic. The activities of MC3T3-E1 cells suggested that the proliferation trend on the micro/nanostructured surfaces was greatly influenced by different crystalline phases, and the highest proliferation rate was obtained on the anatase/rutile surface, followed by the anatase; but the cell differentiation and extracellular matrix mineralization were almost the same among them. After ultrathin HA modification on the micro/nanostructured surfaces with different crystalline phases, it exhibited similar proliferation trend as the original surfaces; however, the cell differentiation and extracellular matrix mineralization were significantly improved. The results indicate that the introduction of ultrathin HA to the micro/nanostructured surfaces with optimized crystalline phase benefits cell proliferation, differentiation and maturation, which suggests a favorable biomimetic microenvironment and provides the potential for enhanced implant osseointegration in vivo.

Structural Relaxation and Crystalline Phase Effects on the Exchange Bias Phenomenon in FeF2/Fe Core/Shell Nanoparticles

AbstractIn this study, the power of first‐principles methods along with molecular dynamics and atomistic Monte Carlo simulations is employed to elucidate the effects of the structural relaxation on the exchange bias (EB) behavior of FeF2/Fe core/shell nanoparticles. The effects of the crystalline phase are also explored by studying the EB features on the related nanoparticles modeled through simple cubic, body centered cubic, and face centered cubic systems. The results indicate that effects of both structural relaxation and crystalline phase on the EB phenomenon are crucial. Noticeable differences are found in the quantitative and qualitative results, as well as in conclusions from studies which, for the sake of simplicity, have used simple cubic crystalline structures for modeling the sample of study instead of its own crystalline model. To compare these results with experimental systems, hysteresis behaviors under field cooling procedures and for a sample made up by a particle diameter distribution D = 4.3 ± 0.7 nm, which is easily affordable at present, are presented. In that sense, this study raises a warning about the conclusions derived from previous works, and offers a suggestion to pay close attention to both the crystalline model and the structural relaxation of the nanoparticle systems exhibiting EB effects.

A DFT study of dimethyl carbonate synthesis from methanol and CO2 on zirconia: Effect of crystalline phases

The reaction mechanism of dimethyl carbonate (DMC) synthesis from methanol and CO2 over cubic (c), tetragonal (t), and monoclinic (m) ZrO2 phases have been investigated by density functional theory (DFT) calculations. The two possible reaction routes have been examined on the three most stable surfaces of zirconia, namely the dry perfect c-ZrO2(1 1 1), t-ZrO2(1 0 1), and m-ZrO2(1¯ 1 1). The Mulliken charge analysis suggested that methanol and CO2 were activated by the Lewis basic sites. Our DFT results showed that the reaction took place through the same route on all three surfaces: 2CH3OH + CO2 → 2CH3O + 2H + CO2 → CH3OCOO + 2H + CH3O → CH3OCO + O + CH3O + 2H → DMC + H2O. In the process, CH3OCOO → CH3OCO + O was the rate-controlling step on the c-ZrO2(1 1 1) and m-ZrO2(1¯ 1 1) surfaces, while CH3OCO + CH3O → DMC was rate-controlling step on the t-ZrO2(1 0 1) surface. The activation free barriers were evaluated on the basis of the rate-controlling steps. The lowerst value was found for the reaction on the t-ZrO2(1 0 1) surface and was equal to 196.4 kJ/mol, while the highest activation free barrier was 274.1 kJ/mol, relative to the reaction on c-ZrO2(1 1 1). Therefore, the results showed that the order of catalytic activity of the dry catalysts was as follows: t-ZrO2 > m-ZrO2 > c-ZrO2. In addition, the catalytic activity of ZrO2 could be determined by the acid-baisic properties of surface and electronic structures. The present work therefore provides a theoretical guidance for designing the hydrated and composite catalysts for DMC synthesis from methanol and CO2.

Preparation of high porosity bricks by utilizing red mud and mine tailing

Due to tremendous size and environmental concerns, management and utilization of red mud and gold tailing have received attention for the last few decades. In the present study, the novel process for utilization of red mud and gold tailing for high porosity brick was proposed and its physical properties were evaluated. By adopting the gelation of slurry method, above 75% apparent porosity; that is hardly obtainable by traditional method, was successfully achieved. Morphologies investigation including pore size distribution revealed that the increasing mixing ratio of gold tailing results in the increasing pore diameter along with changing into closed cell structure. In addition, effect of crystalline phase on thermal conductivity was evaluated and found the dominant effect of quartz phase on thermal conductivity. As a result, increasing of gold tailing leads to increasing of thermal conductivity. Finally, the thermal conductivity of present system was successfully estimated by using Ashby-Glicksman model considering the different type of cell structure.

The effect of crystalline phase (anatase, brookite and rutile) and size on the photocatalytic activity of calcined polymorphic titanium dioxide (TiO2)

The effect of thermal treatment on the morphology (crystalline phase and size) and photocatalytic activity of freshly prepared TiO2 nano-powder is communicated. TiO2 nano-powders, prepared by hydrolyzing titanium tetraisopropoxide at room temperature, were all dried at 382 K and subsequently calcined at different temperatures, for 1 h, up to 1172 K. Raman analysis of each thermally treated sample exhibited different titania phase structures. Up to 772 K a mixture of brookite and anatase phases was observed, while a mixture of all three phases, i.e. anatase, brookite and rutile, was observed at 872 K, with a rutile only phase at 1097 K and above. The photocatalytic activity of all samples was assessed by means of the photocatalytic degradation of methyl orange dye (MeO). All anatase-brookite compositions exhibited high photocatalytic activity with the rate of degradation decreasing with increasing calcination temperature, which coincides with (i) a slight increase of the anatase phase, (ii) a slight decrease of the brookite phase, and (iii) a gradual increase of the crystallite size of all phases. The greatest photocatalytic activity was observed for the sample calcined at 382 K, which contained the highest amount of brookite (in the presence of anatase as the dominant phase), while the lowest rate was observed for the pure rutile sample.

Fluxless flip-chip bonding using a lead-free solder bumping technique

With the LHC exceeding the nominal instantaneous luminosity, the current barrel pixel detector (BPIX) of the CMS experiment at CERN will reach its performance limits and undergo significant radiation damage. In order to improve detector performance in high luminosity conditions, the entire BPIX is replaced with an upgraded version containing an additional detection layer. Half of the modules comprising this additional layer are produced at DESY using fluxless and lead-free bumping and bonding techniques. Sequential solder-jetting technique is utilized to wet 40-μm SAC305 solder spheres on the silicon-sensor pads with electroless Ni, Pd and immersion Au (ENEPIG) under-bump metallization (UBM). The bumped sensors are flip-chip assembled with readout chips (ROCs) and then reflowed using a flux-less bonding facility. The challenges for jetting low solder volume have been analyzed and will be presented in this paper. An average speed of 3.4 balls per second is obtained to jet about 67 thousand solder balls on a single chip. On average, 7 modules have been produced per week. The bump-bond quality is evaluated in terms of electrical and mechanical properties. The peak-bump resistance is about 17.5 mΩ. The cross-section study revealed different types of intermetallic compounds (IMC) as a result of interfacial reactions between UBM and solder material. The effect of crystalline phases on the mechanical properties of the joint is discussed. The mean shear strength per bump after the final module reflow is about 16 cN. The results and sources of yield loss of module production are reported. The achieved yield is 95%.

Steam reforming of acetic acid using Ni/Al2O3 catalyst: Influence of crystalline phase of Al2O3 support

Ni-based catalysts supported on various alumina supports with different crystalline phases (γ-, α-, θ- and δ-Al2O3) were prepared and the effects of crystalline phases on the catalytic performance towards acetic acid steam reforming (AASR) were investigated. An acetic acid conversion of nearly 100% was observed in all the four catalysts, and their hydrogen selectivities were in the following order: Ni/α-Al2O3 (90%) > Ni/γ-Al2O3 (79%) > Ni/δ-Al2O3 (53%) > Ni/θ-Al2O3 (25%). Using different characterization methods, the inner relationship between catalyst crystalline phase and catalytic properties was determined. Through TEM, H2-TPR and XPS characterization, Compared with α-Al2O3, on the surface of other crystalline phases of Al2O3 support were formed NiAl2O4 which indicated stronger interaction intensity between these supports and Ni., and that would reduce the formation of metallic Ni. It was confirmed that metallic Ni played a core role of catalytic AASR. More metallic Ni content caused better CC bonds and CH bonds breaking capability and eventually enhanced the selectivity towards hydrogen. That would be the key reason for Ni/α-Al2O3 showed best hydrogen selectivity among these four catalysts.

Effect of crystalline phase on the dielectric and energy storage properties of poly(vinylidene fluoride)

The crystal structure shows great influence on dielectric and energy storage performance of poly(vinylidene fluoride) (PVDF) films. In this paper, a γ-phase PVDF film was fabricated by crystallization of PVDF from a DMF solution through a solution-casting method and a quenching treatment. The influences of crystalline phases on the dielectric and energy storage properties of the films were studied. It has been found that, compared with common α- and β-phase, the obtained γ-phase PVDF film presents much higher relative permittivity of about 9.8 in a 1 kHz electric field. The ferroelectric hysteresis loop investigation indicates that the γ-phase PVDF film exhibits much slimmer polarization–electric field hysteresis loops than α- and β-phase PVDF films and a high energy efficiency more than 72 % is obtained. This γ-phase PVDF film also shows low leakage current at high working voltage, which is more desirable and promising for high performance pulse discharge capacitor application.

Effect of Crystalline Phase and Composition on the Catalytic Properties of PdSn Bimetallic Nanoparticles in the PROX Reaction

We present a synthetic strategy for the preparation of palladium–tin alloy and intermetallic nanoparticles. Complexes of palladium(II) and tin(IV) precursors in oleylamine were thermally decomposed in an organic solution in the presence of reducing moieties, leading to the formation of monodispersed nanoparticles with varying crystallographic structures. We found that the nanoparticles crystalline structure closely follows the bulk material phase diagram. The nanoparticles were supported on Al2O3 and their reactivity tested as catalysts for the preferential oxidation of CO in excess of hydrogen (PROX). Different Pd/Sn and O2/CO ratios have been investigated, and the structure–reactivity correlation highlighted. With increasing tin content, the CO ignition temperature remarkably lowers and the CO conversion rate increases, up to the formation of intermetallic phases that concurrently determine a reduction in the catalyst activity; the selectivity of the pure palladium references is preserved.

A novel chromic oxide catalyst for NO oxidation at ambient temperature

Chromic oxide catalysts were prepared by ammonia precipitation method and first used in NO oxidation to NO2 at ambient temperature. After calcination at 300 °C, the catalyst exhibited higher catalytic activity with 100% conversion of NO and significantly longer lifetime than activated carbon or activated carbon fiber that has been reported so far. The effects of crystalline phases and surface hydroxyl groups on the activity as well as the durability of catalysts in NO oxidation were investigated by XRD, HRTEM, TG, XPS, Raman and DRIFT techniques. The results indicated that the amorphous structure and surface hydroxyl groups together contributed to the high catalytic activity and long-time stability of the catalysts. The promoting effect of surface hydroxyl groups for long-time stability was confirmed by the alkaline treatments of amorphous chromic oxide catalysts.

Effects of crystalline phase and morphology on the visible light photocatalytic H2-production activity of CdS nanocrystals

Visible light photocatalytic H2-production from aqueous solutions is of great importance for its potential application in converting solar energy into chemical energy. In this study, a series of CdS nanostructures with different contents of wurtzite (WZ) and zinc blende (ZB) phases were successfully synthesized by a simple solvothermal route in an ethylenediamine and ethylene glycol mixed solution. The solvent volume ratio of ethylenediamine in the mixed solution (R) exhibited an obvious influence on the crystalline phase and morphology of the resulting CdS products. With increasing R, the percentage of wurtzite first increased and then decreased, whilst the morphology changed from nanoparticles to multi-armed nanorods, and finally to long rods and sheets. The prepared multi-armed CdS nanorod samples showed especially high and stable photocatalytic H2-production activity with Pt (0.25 wt%) as a co-catalyst and lactic acid aqueous solution as a sacrificial reagent under visible light irradiation. The optimized CdS nanorods with the highest percentage (64%) of the WZ phase exhibited a high H2-production rate of 231.4 μmol h(-1) (about 16.6 times higher than that of CdS nanoparticles with a low percentage (38.4%) of WZ CdS) and with a quantum efficiency (QE) of 28% at 420 nm. This high photocatalytic H2-production activity could be attributed to the results of the positive synergistic effects of the hexagonal WZ phase and morphology of multi-armed nanorods.

Effects of Crystalline Phase and Particle Size on the Properties of Plate-Like Fe2O3 Nanoparticles during γ- to α-Phase Transformation

Plate-like Fe2O3 nanoparticles were prepared in microporous regenerated cellulose films and then completely removed from the cellulose matrix by calcination. Crystallite size and properties variations of the nanosized Fe2O3 during γ- to α-phase transformation were investigated. The γ-Fe2O3 nanoparticles with an initial particle size of 24 nm increased from 26 to 83 nm with an increase of the calcination temperature from 350 to 800 °C, and the phase transformation temperature was about 500 °C. The nanoparticles made at 350 and 450 °C exhibited superparamagnetic properties with the corresponding blocking temperature (TB) of about 83 and 80 K. The nanoparticles made at 500, 600, and 700 °C not only exhibited Curie transitions with TB's of about 77, 54, and 15 K but also had Morin transitions from a pure antiferromagnet to a ferromagnet occurring at about 238, 240, and 246 K, respectively. However, the nanoparticles made at 800 °C only gave a clear Morin transition from a pure antiferromagnet to a ferromagnet at about 250 K. Furthermore, the nanoparticles also displayed different electrochemical properties.

Effects of crystalline phase on the biological properties of collagen–hydroxyapatite composites

The objective of this study was to investigate the effects of spatial structure and crystalline phase on the biological performance of collagen–hydroxyapatite (Col–HA) composite prepared by biomineralization crystallization. Two types of Col–HA composites were prepared using mineralization crystallization (MC composites) and pre-crystallization (PC composites), respectively. Structural characteristics were analyzed by scanning electron microscopy and transmission electron microscopy. Surface elemental compositions were measured by electron spectroscopy for chemical analysis (ESCA). These composites were used in in vivo repair of bone defects. The effects of the crystalline phase on the biological performance of Col–HA composites were investigated using radionuclide bone scan, histopathology and morphological observation. It was observed that in MC composites, HA was located on the surface of the collagen fibers and aggregated into crystal balls, whereas HA in PC composites was scattered among the collagen fibers. ESCA showed that phosphorus and calcium were 8.99% and 17.56% on MC composite surface, compared with 4.39% and 5.86% on the PC composite surface. In vivo bone defect repair experiments revealed that radionuclide uptake was significantly higher in the area implanted with the PC composite than in the contralateral area implanted with the MC composite. Throughout the whole repair process, the PC composite proved to be superior to the MC composite with regard to capillary-forming capacity and the amount of newly formed bone tissue. So it could be concluded that HA placement on collagen fibers affected the biological performance of Col–HA composites. Pre-crystallization made HA scattered among collagen fibers, creating a better structure for bone defect repair in comparison with MC Col–HA composites.

Effect of crystalline phases on deformation and warm formability of a bulk metallic glass composite within supercooled liquid region

The thermal and mechanical properties of a Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 bulk metallic glass composite (BMGC) have been investigated. The thermal properties were determined by using a differential scanning calorimeter (DSC), while the phase and composition analysis of crystalline precipitates within glassy matrix were carried out by X-ray diffraction (XRD). The deformation behavior has also been investigated through a series of compression tests performed under several strain rates between 10−4s−1 and 10−2s−1 at various temperatures within supercooled liquid region (SLR). This BMG composite was found to have improved high temperature strength compared to other Zr-based monolithic BMGs. The in situ formed crystalline phases are believed to hinder the viscous flow of glassy matrix to raise the high temperature strength, compensating more the minor softening of crystalline phases at higher temperatures within the SLR. The warm formability of the composite was also estimated by applying the dynamic materials model (DMM) and the results were verified by subsequent laboratory-scale extrusion tests.