Surface Crystallization Behavior Research Articles

The surface crystallization behavior of reactive plasma sprayed TiCN coating with Cr addition

TiCrCN coatings were sprayed by mixing aggregated Ti-graphite powders and metallic Cr powders with different weight ratios. The microstructure and surface crystallization behavior were researched. The results confirmed that the phases in the TiCN coating were TiC0.7N0.3 + TiC0.8 N0.2 + Ti3O + CNx + graphite (unreacted). In contrast, the TiCrCN coating included metallic Cr and TiCrCN in addition to TiC0.7N0.3, TiC0.8N0.2, Ti3O, CNx, and unreacted graphite. With the increase of Cr, the content of Cr phase increased, coupling with TiC0.7N0.3 and Ti3O decreasing. The addition of Cr decreased the cracks and pores in the sprayed TiCN and TiCrCN coatings, and changed the surface crystallization behavior from dendritic crystals to columnar crystals.

Effect of TiO2 content on crystallization behavior of CaO–Al2O3–SiO2–ZnO glass-ceramic glaze

In this study, TiO2 was substituted as a nucleating agent to apply CaO–Al2O3–SiO2–ZnO (CASZ)-based glass to a high-hardness crystallized glaze, and the crystallization behavior and hardness of the glaze were observed with respect to the amount of TiO2 substitution. X-ray diffraction and scanning electron microscopy analyses revealed that as the TiO2 substitution increased, a titanite crystal phase was formed in the existing anorthite crystal phase, and the crystallinity of the glaze rapidly increased. In particular, the highest crystallinity of 83.8% was observed for 12.5 wt% TiO2 substitution. The activation energy and Avrami exponent (n) of the glaze were calculated via non-isothermal analysis using differential thermal analysis, and surface crystallization behavior of n ≤ 2.5 was observed for all mixing ratios. The density of the glaze increased from 2.33 to 2.80 g cm−3 as the TiO2 substitution increased. The hardness of the glaze showed the lowest value (3.12 GPa) for the sample without TiO2 substitution and increased rapidly to 6.33 GPa or higher in the TiO2 substitution specimens.

Design of FeSiBPCu soft magnetic alloys with good amorphous forming ability and ultra-wide crystallization window

The Fe81.3Si4B13–xPxCu1.7 soft magnetic alloys with high Cu and proper P elements addition were synthesized with the aim of ensuring the amorphous forming ability (AFA) while expanding the crystallization window (CW). It is found that the atomic ratio of P/Cu of ∼3 is advantageous for AFA whereas a small amount of P addition promotes the precipitation of α-Fe grains and excessive P addition induces surface crystallization behavior of the present alloys. High Cu concentration can expand the annealing temperature (Ta) window whereas proper P addition effectively expands the annealing time (ta) window. The Fe81.3Si4B8P5Cu1.7 soft magnetic alloy was successfully synthesized with a large Ta window of up to 130 °C and ta window of 90 min, which is a breakthrough for nanocrystalline alloys with high saturation magnetization. Microstructure analysis reveals that the ultra-wide CW is related to the unique nucleation mechanism, that is, the α-Fe grains are precipitated attaching to the Cu or CuP clusters and enveloping the Cu clusters, resulting in the high number density of α-Fe nanocrystals. The ultra-wide CW promises the potential material in flexibly choosing the annealing process according to the performance.

Improving the Bs and soft magnetic properties of Fe-based amorphous ribbons by manipulating the surface crystallization behavior

Improving the Bs and soft magnetic properties of Fe-based amorphous ribbons by manipulating the surface crystallization behavior

Preparation and characterization of photothermal polyurethane/zirconium carbide fibrous membranes via electrospinning

Human activities in cold climates are more and more frequent. But, an efficient strategy to maintain the human body temperature is still a challenging work. In this paper, we propose a photothermal polyurethane/zirconium carbide(PU/ZrC) fibrous membrane assembled via electrospinning technique, which can make up for heat lost from the human body by absorbing and converting light energy. When the content of ZrC nanoparticles (Nps) was increased to 8%, the surface temperature of the composite fibrous membrane was increased to 66.5 °C after illumination for 150 s under a Xenon lamp. Besides, the surface morphologies, crystallization behavior, thermal property, mechanical property, wettability and air permeability of the fibrous membranes were also evaluated. The morphology of the fibrous membranes exhibited that mesh-like fibers were densely aligned and the hydrophobicity of the PU/ZrC composites could be improved when ZrC Nps were added. Moreover, the PU/ZrC membrane with low content of ZrC has outstanding mechanical properties and good air permeability. Our results indicate that the PU/ZrC membranes may have promising potentials in the applications of personal thermal management textiles.

Surface oxidation and crystallization of FeNi-Based soft magnetic nanocrystalline and amorphous nanocomposite alloys

In this work, we present characterization of surface oxidation and crystallization behavior of Metal Amorphous Nanocomposite (MANC) (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 alloys via complementary x-ray diffraction, electron microscopy, and x-ray photoelectron spectroscopy techniques. An adherent amorphous oxide of roughly 15–20 nm in thickness is observed on the wheel side of the ribbon, enriched in Fe relative to Ni and with significant content of Si and Nb as would be expected based upon a comparison of the Gibbs free energy of formation of the stable oxide phases. The amorphous character of the oxide is likely to result from the significant Si-content coupled with the amorphous and nanocrystalline character of the underlying metallic layer. Higher density of FeNi-enriched nanocrystals is also observed within ∼100 nm of the wheel-side surface, presumably due to reduction in local glass former concentration. A rough, crystalline copper oxide layer is also present and forms through contact between the copper wheel and the solidifying melt during the rapid solidification process. On the air side of the ribbon, a crystalline oxide layer of ∼15–20 nm is formed as well as intergranular oxidation that penetrates along the grain boundaries between highly textured surface crystallites of ∼50–100 nm in size. The crystalline nature of the oxide on these surfaces is asserted to result from the lack of significant Si-content and the pre-existing surface crystallites that form during the rapid solidification process which promote a crystalline oxide surface layer. These results shed new insights into the details of surface oxidation and can help to inform processing and alloy composition adjustments which seek to tailor surface properties.

Crystal Growth Behavior, Nanometer Microstructure, and Mechanical Properties of Diopside-Based Glass-Ceramics.

In this study, to increase the light transmittance of diopside type crystallized glass, crystals with size of less than 100 nm, which is smaller than the visible light wavelength, were generated in the specimen. For this purpose, the so-called two-step process encompassing heat treatment at the nucleation temperature followed by heating the crystal at the crystal growth temperature was employed. The crystallization behavior of the prepared specimen was studied and the optical and mechanical properties were investigated according to the heat treatment conditions. The glass used in the experiment was CaO-MgO-2SiO₂, which is a stoichiometric composition of diopside crystals. Heat-treating temperatures for nucleation and crystal growth were determined by a nonisothermal thermal analysis using Differential Thermal Analysis (DTA). The most suitable heattreating conditions were nucleation at 761 °C/6 h and crystal growth at 880 °C/1 h. The generated diopside crystal size was below 100 nm on average and the light transmittance was as high as ~75% for most of the specimens and the parent glass specimen showed higher light transmittance than that of conventional commercialized semitransparent crystallized glass products. The bending strength of diopside-based glass-ceramics was 30 MPa and the fracture energy was 1.56 N/mm. The Avrami constant calculated from the Kissinger equation and the Augis-Bennett equation was 1.38 and the activation energy was 355.63 kJ/mol, and these value indicate surface crystallization behavior.

Nanometer Scale Microstructure and Optical Properties of BaO-TiO₂-SiO₂ System-Based Glass-Ceramics.

The fresnoite phase, one of the crystals obtainable in the BaO-TiO₂-SiO₂ (BTS) system, is a material with excellent nonlinear optical properties. In this study, glass-ceramic containing nanometer scale fresnoite crystal was prepared by controlling the heat-treatment process from a BTS system, and its properties were analyzed. BTS glasses were prepared by conventional melting and quenching method. The heat treatment conditions were investigated by the non-isothermal analysis method using DTA. The formation of fresnoite crystals and the change of crystallinity according to heat treatment temperature were investigated by a XRD analysis. The glass-ceramics prepared in this study had fine crystal grains less than 100 nm in size and showed surface crystallization behavior growing from the surface to the inside. The transmittance of the prepared specimen in the range of visible light was measured up to 77%. The photoluminescence (PL) intensity of specimen was remarkably high at 470 nm and the emitted light has a blue and white light characteristic as displayed in the CIE coordinates.

Surface crystallization behavior of calcium carbonate in the presence of SMPs secreted by SRB

Surface crystallization of insoluble carbonate poses a serious problem for marine equipment industries which can be seriously influenced by soluble microbial products (SMPs). In Here, the effects of SMPs secreted by sulfate-reducing bacteria on the formation of CaCO3 were investigated by monitoring the crystallization rates and crystal polymorphs and morphologies. When 8.95 mg/L of SMP was added, vaterite and calcite were formed at the initial stage. This could be partly attributed to the formation of SMP and Ca2+ complexes, which provided a nucleation site for calcite. Simultaneously, crystallization by particle attachment promoted the increase of the crystallization mass density in the early stage of crystallization. As the concentration increased to 17.90 mg/L, a larger proportion of vaterite was stabilized. However, a further increase of SMP concentration to 44.76 mg/L did not enhance the proportion of vaterite and a different morphology of elongated calcite was formed. All investigated concentrations of experiments indicate that lower concentrations of SMP promotes calcite nucleation, and higher concentrations inhibit the formation of vaterite. However, an inverse relationship still exists between the concentration of SMP and the amount of surface crystallization of calcium carbonate.

Understanding Dissolution and Crystallization with Imaging: A Surface Point of View.

The tendency for crystallization during storage and administration is the most considerable hurdle for poorly water-soluble drugs formulated in the amorphous form. There is a need to better detect often subtle and complex surface crystallization phenomena and understand their influence on the critical quality attribute of dissolution. In this study, the interplay between surface crystallization of the amorphous form during storage and dissolution testing, and its influence on dissolution behavior, is analyzed for the first time with multimodal nonlinear optical imaging (coherent anti-Stokes Raman scattering (CARS) and sum frequency generation (SFG)). Complementary analyses are provided with scanning electron microscopy, X-ray diffraction and infrared and Raman spectroscopies. Amorphous indomethacin tablets were prepared and subjected to two different storage conditions (30 °C/23% RH and 30 °C/75% RH) for various durations and then dissolution testing using a channel flow-through device. Trace levels of surface crystallinity previously imaged with nonlinear optics after 1 or 2 days of storage did not significantly decrease dissolution and supersaturation compared to the freshly prepared amorphous tablets while more extensive crystallization after longer storage times did. Multimodal nonlinear optical imaging of the tablet surfaces after 15 min of dissolution revealed complex crystallization behavior that was affected by both storage condition and time, with up to four crystalline polymorphs simultaneously observed. In addition to the well-known α- and γ-forms, the less reported metastable ε- and η-forms were also observed, with the ε-form being widely observed in samples that had retained significant surface amorphousness during storage. This form was also prepared in the pure form and further characterized. Overall, this study demonstrates the potential value of nonlinear optical imaging, together with more established solid-state analysis methods, to understand complex surface crystallization behavior and its influence on drug dissolution during the development of amorphous drugs and dosage forms.

Influence of the Tungsten Content on Surface Properties of Electroless Ni-W-P Coatings

Ternary Ni-W-P films were produced by electroless deposition using baths with different tungsten concentrations. After deposition, the coated surfaces were annealed at 400°C for 1h. Surface morphology and film composition in the as-plated condition were assessed by SEM and EDS analyses, respectively. The crystalline phases after annealing were investigated by X-ray diffraction (XRD). Nanoindentation tests were performed to assess the mechanical properties of the deposited films. Surface roughness was determined by confocal laser scanning microscopy (CLSM). Friction coefficient was evaluated by reciprocating were tests in a nanotribometer. The corrosion behavior was evaluated by potentiodynamic polarization curves. The results showed that the surface morphology, crystallization behavior and corrosion resistance were affected by the tungsten content in the film. The best corrosion performance was obtained for the ternary films after annealing. Hardness, surface roughness and friction coefficient were dependent of the tungsten concentration in the film.

Surface crystallization behavior during thermal processing of low-photoelastic ZnO–SnO–P2O5 glasses

Pb-containing glasses such as the PbO–SiO2 series are useful in optical devices because of their low-photoelastic constants (PECs); however, the toxic Pb component in these glasses is problematic. Transparent ternary ZnO–SnO–P2O5 glasses are potential substitutes for low-PEC Pb-containing glasses, but their thermal behavior is not well understood, which inhibits their ability to be drawn into fibers. Herein, we report the surface crystallization behavior of transparent ternary ZnO–SnO–P2O5 glasses, including those with low-PEC compositions, heated under isothermal conditions to temperatures above their glass-transition temperatures. The crystallization conditions for low-PEC phosphate glasses during their thermal processing into shapes of optical modules were deduced. The crystalline compounds precipitated on the surfaces were investigated via X-ray diffraction analysis, micro-Raman spectroscopy, and microscopic observations. A time–temperature–transformation diagram was constructed on the basis of the thermal stability of the glasses. We expect that this enhanced understanding of the crystallization behavior induced by the reshaping process will enable fabrication of precise polarization control devices with low PECs, such as optical-fiber current sensors, optical lenses, and filters.

Surface flashover performance of phenolphthalein modified LDPE in vacuum

Since surface flashover of insulators in vacuum restricts the operation of the power equipment, improvement of surface flashover performance is of considerable importance in various fields. Previous studies show that surface flashover performance is closely related to the trap parameters of materials. In this paper, the crystallization behavior of low density polyethylene (LDPE) is modified by phenolphthalein. It results in the change of the trap parameters, leading to the enhancements in surface flashover performance. Results of differential scanning calorimeter (DSC) and scanning electron microscope (SEM) show that the crystallization behavior of LDPE is greatly changed by phenolphthalein. The crystallinity increases initially and then decreases with the increase of phenolphthalein concentration, and its maximum value occurs at 0.4 wt%. The spherulite size of LDPE composites decreases obviously with the increasing phenolphthalein concentration. The results of thermally stimulated current (TSC) show that both the shallow trap (γ peak) and the deep trap (α peak) become deeper with the increase of phenolphthalein concentration. Furthermore, the impulse and dc surface flashover voltages present the optimum values at 1 wt% phenolphthalein concentration, which can be enhanced by 30.8% and 48.4%, respectively. It is concluded that LDPE with the smaller spherulite size indicates the deeper trap and the better surface flashover performance. This paper reveals the relationship between surface flashover performance and crystallization behavior of LDPE, and proposes a new method to enhance the surface flashover performance of semi-crystalline polymers in vacuum.

In situ AFM study of near‐surface crystallization in PET and PEN

ABSTRACTThe surface crystallization behavior of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) spin‐coated thin films was compared by means of atomic force microscopy (AFM) with an in situ heating stage. As the films were heated up stepwise, characteristic surface crystals appeared at a crystallization temperature (Tc) in the near‐surface region which is about 15 °C under the bulk Tc, and were replaced by bulk crystals when the temperature was increased to the bulk Tc. In the case of films whose thickness is less than 70 nm (PET) and 60 nm (PEN), significant increases in the bulk Tc were observed. Scanning force microscopy (SFM) force‐distance curve measurements showed that the glass transition temperature (Tg) of the near‐surface region of PET and PEN were 22.0 and 26.6 °C below their bulk Tg (obtained by DSC). After the onset of surface crystallization, edge‐on and flat‐on crystals appeared at the free surface of PET and PEN thin films, whose morphologies are very different to those of the bulk crystals. Although the same general behavior was observed for both polyesters, there are significant differences both the influence of the surface and substrate on the transition temperatures, and in morphology of the surface crystals. These phenomena are discussed in terms of the differences in the mobility of polymer chains near the surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44269.

Crystallization and thermal expansion behavior of lithium zinc silicate sealing glass

Effect of heat treatment schedule on the crystallization and thermal expansion behavior of a lithium zinc silicate glass system was investigated by differential scanning calorimeter (DSC), X-ray diffraction, and linear thermal expansion test. Two well-defined crystallization exothermic peaks were observed from the DSC trace. According to the apparent activation energies and avrami parameter values calculated from the two crystallization exothermal peaks, the first crystallization exothermal peak was attributed to a combining surface and internal crystallization behavior, while the second one was found to be internal crystallization. Additionally, the phase evolution and the thermal expansion behavior with increasing heat treatment temperature were found to be closely related. Interestingly, it was found in comparison with previous reports that addition of CaO varies the phase composition of the resulting glass–ceramic in an opposite way to K2O and the deep rooted reason has been discussed which may cast light on the modulation of properties of glass–ceramic involved crystalline phase of quartz or cristobalite. At last, average thermal expansion coefficient of 7.99–15.38×10−6K−1 in the temperature range of 25–400°C has been obtained with different heat treatment schedules.

Effects of soy-to-milk protein ratio and sucrose fatty acid ester addition on the stability of ice cream emulsions

The protein composition and emulsifier adsorbed at the oil/water interface are very important in controlling the stability of fat droplets. In this study, the effect of soy-to-milk protein ratio in the presence or absence of sucrose fatty acid ester on the stability of ice cream emulsions was investigated. Parameters such as particle size distribution, dynamic surface pressure, surface protein adsorption, rheological properties and crystallization behavior of fat in the bulk and emulsified state were determined. The results indicated that destabilization of fat droplets depended on the protein surface adsorption activity, protein–protein and protein-sucrose fatty acid ester interactions at the interfacial layers. The addition of soy protein isolate significantly increased the flocculation of fat droplets during pasteurization. Emulsions containing sucrose fatty acid ester were distinguished by a higher partial coalescence degree (19.8–252.7%) of fat droplets compared to emulsions without sucrose fatty acid ester (5.5–37.3%) with the same protein composition. The particle size and adsorbed protein results showed a direct negative relationship between protein surface coverage and partial coalescence degree for emulsions with sucrose ester. The increased protein coverage when the soy-to-milk protein ratio was above 5:5 probably resulted from the enhanced protein–protein interactions. The supercooling needed for detection of crystalline fat was found to increase with the increase in soy-to-milk protein ratio up to 7:3. However, no significant correlation was found between the proportion of crystallized fat content and partial coalescence degree. These findings provided a theoretical basis for controlling the stability of aerated food emulsions with soy/milk protein mixture.

Characterization of surface chemistry and crystallization behavior of polypropylene composites reinforced with wood flour, cellulose, and lignin during accelerated weathering

In this study, six groups of polypropylene composites reinforced with wood flour (WF), cellulose, and lignin at different loading levels were exposed in a QUV accelerated weathering tester for a total duration of 960h. The changes in surface morphology, chemistry, and thermal properties of weathered samples were characterized by atomic force microscope (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetric (DSC), respectively. The flexural properties of all samples were tested after different durations of weathering. The results showed that: (1) the surface roughness of all samples increased after weathering; (2) composites containing lignin showed less loss of flexural strength and modulus and less roughness on weathered surface compared with lignin-free composites, indicating the functions of stabilization and antioxidation of lignin; (3) the crystallinity of PP increased in all weathered samples due to chain scissions and recrystallization; (4) ATR-FTIR and XPS analyses demonstrated in detail that significant changes occurred in surface chemistry, accompanied by the photodegradation and photo-oxidation of lignin and cellulose with prolonged weathering time.

Influence of amorphous phase separation on the crystallization behavior of glass-ceramics in the BaO–TiO2–SiO2 system

The possible role of a prior amorphous phase separation on the subsequent crystallization has been the topic of vigorous debates over the last decades and has not yet been clarified, especially regarding the role of the interfaces created by the phase separation. This study proposes to focus on the interplay between a prior amorphous phase separation and the crystallization of fresnoite in the BaO–TiO2–SiO2 system. The crystallization behavior of a non-stoichiometric composition inside the miscibility gap (called APS) is compared with the stoichiometric composition (called FRES) and a non-stoichiometric composition outside the miscibility gap (called NoAPS). The crystallization mechanisms are compared using differential thermal analysis (DTA) by calculating the Avrami parameters and the activation energies as a function of the particle size. The DTA study shows that the two non-stoichiometric compositions exhibit a pronounced surface crystallization behavior whereas FRES undergoes bulk nucleation. This is supported by a multi-scale microstructure characterization. Furthermore, this study demonstrates that the amorphous phase separation and the associated interfaces do not play any significant role in the nucleation step. Moreover, transmission electron microscope (TEM) and local orientation measurements show that the growth of the dendrites is not hindered by the SiO2-rich droplets. The final stage of crystallization of APS is tentatively explained by two composition effects that must be further investigated: the viscosity effect and the formation of a eutectic.

Evaluation of Crystallization Behavior on the Surface of Nifedipine Solid Dispersion Powder Using Inverse Gas Chromatography

To investigate crystallization behavior on the surface of amorphous solid dispersion powder using inverse gas chromatography (IGC) and to predict the physical stability at temperatures below the glass transition temperature (T (g)). Amorphous solid dispersion powder was prepared by melt-quenching of a mixture of crystalline nifedipine and polyvinylpyrrolidon (PVP) K-30. IGC was conducted by injecting undecane (probe gas) and methane (reference gas) repeatedly to the solid dispersion at temperatures below T (g). Surface crystallization was evaluated by the retention volume change of undecane based on the observation that the surface of the solid dispersion with crystallized nifedipine gives an increased retention volume. On applying the retention volume change to the Hancock-Sharp equation, surface crystallization was found to follow a two-dimensional growth of nuclei mechanism. Estimation of the crystallization rates at temperatures far below T (g) using the Avrami-Erofeev equation and Arrhenius equation showed that, to maintain its quality for at least three years, the solid dispersion should be stored at -20°C (T (g) - 65°C). IGC can be used to evaluate crystallization behavior on the surface of a solid dispersion powder, and, unlike traditional techniques, can also predict the stability of the solid dispersion based on the surface crystallization behavior.

Crystallization behavior and mechanical properties of erbium oxide coatings fabricated by pulsed magnetron sputtering

Erbium oxide coatings were prepared by mid-frequency pulsed magnetron sputtering at different sputtering powers and substrate temperatures. Atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and nanoindentation were used to investigate surface morphologies, compositions, crystallization behavior, and mechanical properties of the coatings, respectively. The thermal stability of the coating structure was also investigated. A monoclinic phase was observed in the erbium oxide coatings prepared at substrate temperatures below 350 °C. A cubic phase was obtained by elevating the temperature to 500 °C. The monoclinic phase coatings deposited at elevated substrate temperatures showed high phase stability. The coatings with a cubic phase exhibited higher hardness and elastic modulus than those with a monoclinic phase, attributable to a narrower bond length distribution and a shorter average bond length.