Regulating crystal phase of TiO_(2) to enhance catalytic activity of Ni/TiO_(2) for solar-driven dry reforming of methane

Ni/TiO_(2) catalyst is widely employed for photo-driven DRM reaction while the influence of crystal structure of TiO_(2) remains unclear.In this work,the rutile/anatase ratio in supports was successfully controlled by varying the calcination temperature of anatase-TiO_(2).Structural characterizations revealed that a distinct TiO_(x) coating on the Ni nanoparticles(NPs)was evident for Ni/TiO_(2)-700 catalyst due to strong metal-support interaction.It is observed that the TiOx overlayer gradually disappeared as the ratio of rutile/anatase increased,thereby enhancing the exposure of Ni active sites.The exposed Ni sites enhanced visible light absorption and boosted the dissociation capability of CH4,which led to the much elevated catalytic activity for Ni/TiO_(2)-950 in which rutile dominated.Therefore,the catalytic activity of solar-driven DRM reaction was significantly influenced by the rutile/anatase ratio.Ni/TiO_(2)-950,characterized by a predominant rutile phase,exhibited the highest DRM reactivity,with remarkable H_(2) and CO production rates reaching as high as 87.4 and 220.2 mmol/(g·h),respectively.These rates were approximately 257 and 130 times higher,respectively,compared to those obtained on Ni/TiO_(2)-700 with anatase.This study suggests that the optimization of crystal structure of TiO_(2) support can effectively enhance the performance of photothermal DRM reaction.

Effects of Additive AlCl_3 on Crystal Phase, Particle Size and Microstructural Parameters of Nanocrystalline TiO_2 Prepared by HF-PCVD

Nanocrystalline TiO2 was prepared by high frequency plasma chemical vapor deposition (HF-PCVD). The effects of additive AlCl3 on crystal phase, particle size and microstructurai parameters of TiO2 nanocrystallites were investigated by X-ray diffraction(XRD) and transmission electron microscopy (TEM). The nanocrystallites obtained experimentally are mixture of anatase and rutile, the uniform diameters of particles are about 30 nm. The phase transformation from anatase to rutile was accelerated by AlCl3, and rutile content is increased from 26.7 wt pct to 53.6 wt pct with increasing of addition of AlCl3 from 0.0 wt pct to 5.0 wt pct. The particle size is reduced and the size distribution becomes very narrow. The crystal lattice constants have the trend to decrease, and celi volumes appear as shrinkable.

Insights into effects of ZrO_(2) crystal phase on syngas‐to‐olefin conversion over ZnO/ZrO_(2) and SAPO‐34 composite catalysts

The utilization of metal oxide‐zeolite catalysts in the syngas‐to‐olefin reaction is a promising strategy for producing C_(2)–C_(4) olefins from non‐petroleum resources.However,the effect of the crystal phase of metal oxides on the catalytic activity of these oxides is still ambiguous.Herein,typical metal oxides(ZnO/ZrO_(2))with different crystal phases(monoclinic(m‐ZrO_(2))and tetragonal(t‐ZrO_(2)))were employed for syngas conversion.The(ZnO/m‐ZrO_(2)+SAPO‐34)composite catalyst exhibited 80.5%selectivity for C_(2)–C_(4) olefins at a CO conversion of 27.9%,where the results are superior to those(CO conversion of 16.4%and C_(2)–C_(4) olefin selectivity of 76.1%)obtained over(ZnO/t‐ZrO_(2)+SAPO‐34).The distinct differences are ascribed to the larger number of hydroxyl groups,Lewis acid sites,and oxygen defects in ZnO/m‐ZrO_(2) compared to ZnO/t‐ZrO_(2).These features result in the formation of more formate and methoxy intermediate species on the ZnO/m‐ZrO_(2) oxides during syngas conversion,followed by the formation of more light olefins over SAPO‐34.The present findings provide useful information for the design of highly efficient ZrO_(2)‐based catalysts for syngas conversion.

Competition between acidic sites and hydrogenation sites in Cu/ZrO_(2) catalysts with different crystal phases for conversion of biomass-derived organics

Oxides with different crystal phases can have important effects on the configuration of surface atoms,which can further affect the distribution of hydrogenation sites and acidic sites as well as the competitions of these varied types of catalytic sites.This could be potentially used to tailor the distribution of the products.In this study,zirconium oxides with different crystal phases supported copper catalysts were prepared for the hydrogenation of the biomass-derived furfural,vanillin,etc.The results showed that both calcination temperature and Cu species affected the shift of zirconia from tetragonal phase to the monoclinic phase.Monoclinic zirconia supported copper catalyst can effectively catalyze the hydrogenation of furfural to furfuryl alcohol via hydrogenation route due to its low amount of Brønsted acidic sites,although the surface area and the exposed metallic Cu surface area were much lower than the tetragonal zirconia supported copper catalyst.Zirconia with tetragonal or tetragonal/monoclinic phases supported copper catalysts contain abundant acidic sites and especially the Br?nsted acidic sites,which catalyzed mainly the conversion of furfural via the acid-catalyzed routes such as the acetalization,rather than the hydrogenation.The acidic sites over the Cu/ZrO_(2)catalyst played more predominant roles than the hydrogenation sites in determining the conversion of the organics like furfural and vanillin.

Crystal Phases and Chemical Stabilities of YSi2 Powders Fabricated from Low and High Purity Si and Y Powders

Y-Si compounds with the composition of Y:Si = 1:2 were fabricated using Yttrium and Silicon raw powders with low and high purity in various atmospheres and temperatures. Although the latest Y-Si phase diagram shows that the α- and β-YSi2 phases are the stable phases for the stoichiometric composition of Y:Si = 1:2, the current experimental results suggest that the high temperature phase with the hexagonal structure, β-Y3Si5, would be the stable phase for this composition, and that the high temperature phase with the orthorhombic structure, β-YSi2, would be the meta-stable phase with high oxygen impurity content. It was demonstrated that YSi2 powders possess much superior chemical stability than Yttrium metal. It was found that the best dispersing solvent was 2-propanol for YSi2 powder.

Crystal phase control and ignition properties of HNS/CL-20 composite microspheres prepared by microfluidics combined with emulsification techniques

Improved controllability and energy density of ignition agents are of great significance for the devel-opment of energetic composite materials.In this study,droplet microfluidics and emulsification tech-niques were combined to prepare HNS/CL-20 composite microspheres with polyglycidyl azide polymer(GAP)as the binder.The influence of binder content on the morphology of microspheres was investi-gated,and the microspheres were characterized and tested for particle size,crystal structure,thermal decomposition,dispersibility,mechanical sensitivity,combustion behavior and detonation performance.The results showed that microspheres prepared with a binder content of 3%had higher sphericity and particle size uniformity.The microspheres retained the crystal structure of both HNS and CL-20(ε-type).Compared with raw HNS,the microspheres had higher apparent activation energy,better safety per-formance,and good dispersibility.The ignition experiments and detonation performance tests show that HNS/CL-20 composite microspheres have excellent ignition performance,obvious combustion flame,and significant energy release effects,which are expected to achieve high energy and high-speed response of the igniter,thus improving the ignition reliability in special environments or systems.

Recent advances in crystal phase induced surface-enhanced Raman scattering

Surface-enhanced Raman scattering(SERS)spectroscopy has emerged as a powerful analytical technique for detecting and identifying trace chemical and biological molecules.In this review,we present an indepth discussion of recent advances in the field of crystal phase manipulation to achieve exceptional SERS performance.Focusing on transition metal dichalcogenides,(hydr)oxides,and carbides as exemplary materials,we illustrate the pivotal role of crystal phase regulation in enhancing SERS signals.By exploring the correlation between crystal phases and SERS responses,we uncover the underlying principles behind these strategies,thereby shedding light on their potential for future SERS applications.By addressing the current challenges and limitations,we also propose the prospects of the crystal phase strategy to facilitate the development of cutting-edge SERS-based sensing technologies.

Effect of Plasma Spheroidization Process on the Microstructure and Crystallographic Phases of Silica, Alumina and Nickel Particles

During the plasma spheroidization process powders undergo different changes in their microstructures and crystal phases. In this paper, simple calculation of heat transfer between the plasma and a suspended particle was performed based on three hypotheses for the purpose of guiding experiments. Experimental investigation of the crystal phases and microstructural changes during the plasma processing was made using silica, alumina and nickel powders as starting materials. It has been revealed from the experimental results that these materials undergo different changes in crystal phases and microstructures, and these changes are essentially determined by the structures, properties and aggregate states of the starting materials.

Crystal phase-controlled growth of PtCu and PtCo alloys on 4H Au nanoribbons for electrocatalytic ethanol oxidation reaction

Crystal phase can greatly affect the physicochemical properties and applications of nanomaterials.However,it stil remains a great challenge to synthesize nanostructures with the same composition and morphology but different phases in order to explore the phase-dependent properties and applications.Herein,we report the crystal phase-controlled synthesis of PtCu alloy shells on 4H Au nanoribbons(NRBs),referred to as 4H-Au NRBs,to form the 4H-Au@PtCu core-shell NRBs.By tuning the thickness of PtCu,4H-PtCu and face-centered cubic(cc)phase PICu(cc-PtCu)alloy shells are successtully grown on the 4H-Au NRB cores.This thickness-dependent phase-controlled growth strategy can also be used to grow PtCo alloys with 4H or fcc phase on 4H-Au NRBs.Significantly,when used as electrocatalysts for the ethanol oxidation reaction(EOR)in alkaline media,the 4H-Au@4H-PtCu NRBs show much better EOR performance than the 4H-Au@fcc-PtCu NRBs,and both of them possess superior performance compared to the commercial Pt black.Our study provides a strategy on phase-contolled synthesis of nanomaterials used for crystal phase-dependent applications.

Crystal phase control in two-dimensional materials

It is the nature of crystals to exist in different polymorphs. The recent emergence of two-dimensional(2 D) materials has evoked the discovery of a number of new crystal phases that are different from their bulk structures at ambient conditions, and revealed novel structure-dependent properties, which deserve in-depth understanding and further exploration. In this contribution, we review the recent development of crystal phase control in 2 D materials, including group V and VI. transition metal dichalcogenides(TMDs), group IVA metal chalcogenides and noble metals. For each group of materials, we begin with introducing the various existing crystal phases and their structure-related properties, followed by a detailed discussion on factors that influence these crystal structures and thus the possible strategies for phase control. Finally, after summarizing the whole paper, we present the challenges and opportunities in this research direction.

Phase separation-hydrogen etching-derived Cu-decorated Cu-Mn bimetallic oxides with oxygen vacancies boosting superior sodium-ion storage kinetics

Understanding the crystal phase evolution of bimetallic oxide anodes is the main concern to profoundly reveal the conversion reaction kinetics and sodium-ion storage mechanisms.Herein,an integrated selfsupporting anode of the Cu-decorated Cu-Mn bimetallic oxides with oxygen vacancies(Ov-BMO-Cu)are in-situ generated by phase separation and hydrogen etching using nanoporous Cu-Mn alloy as selfsacrificial templates.On this basis,we have elucidated the relationship between the phase evolution,oxygen vacancies and sodium-ion storage mechanisms,further demonstrating the evolution of oxygen vacancies and the inhibition effect of manganese oxides as an“anchor”on grain aggregation of copper oxides.The kinetic analyses confirm that the expanded lattice space and increased oxygen vacancies of cycled Ov-BMO-Cu synergistically guarantee effective sodium-ion diffusion and storage mechanisms.Therefore,the Ov-BMO-Cu electrode exhibits higher reversible capacities of 4.04 mA h cm^(-2)at 0.2 mA cm^(-2)after 100 cycles and 2.20 m A h cm^(-2)at 1.0 mA cm^(-2)after 500 cycles.Besides,the presodiated Ov-BMO-Cu anode delivers a considerable reversible capacity of 0.79 m A h cm^(-2)at 1.0 mA cm^(-2)after 60 cycles in full cells with Na_(3)V_(2)(PO_(4))_(3)cathode,confirming its outstanding practicality.Thus,this work is expected to provide enlightenment for designing high-capacity bimetallic oxide anodes.

Crystal phase engineering of electrocatalysts for energy conversions

Crystal phase is an intrinsic structural parameter to determine the physicochemical properties and functionalities of materials.The unconventional phases of materials with distinct atomic arrangements from their thermodynamically stable phases have attracted enormous attention.Phase engineering has recently made fruitful achievements in electrocatalysis field to optimize the performance of various electrochemical reactions.In this review,theoretical and experimental advances made in phase engineering of electrocatalysts are summarized.First,we introduce basic understanding on crystal phases of catalysts to show the dialectical relationship between bulk phase and surface catalytic layer,and highlight the multiple functions of phase engineering in catalysis studies.We then describe phase-controlled synthesis of materials through various experimental methods such as wet-chemical method,phase transition,and template growth.As a focus,we discuss the wide usage of phase engineering strategy in different kinds of electrocatalytic materials,and particular emphasis is given to establishment of reasonable crystal phase-activity relationship.Finally,we propose several future directions for developing more desirable electrocatalysts by rational crystal phase design.

Synthesis of YAG∶Ce^(3+) Phosphor by Polyacrylamide Gel Method and Promoting Action of α-Al_2O_3 Seed Crystal on Phase Formation

YAG： Ce^3 ＋ phosphor particles were prepared using polyacrylamide gel method. The structure evolution of powders during annealing process was followed by X-ray diffraction determination. It is found that some intermediate phases, including θ-Al2O3, YAM and YAP, are formed when calcining polyacrylamide gel, however, the pure YAG phase can be formed directly when calcining polyacrylamide gel with α-Al2O3 as seed crystal. These facts show that the existence of α- Al2O3 seed crystal can block the formation of θ-Al2O3, YAM and YAP, and accelerate its reaction with Y2O3 to form YAG phase directly at lower temperature. The emission peak of prepared YAG ： Ce^3 ＋ phosphor is wide with maximum at 550 nm and the exitation band has two peaks, the major one is around at 460 nm, which matches the blue emission of GaN LED and is suitable for the assemble of white LED. Some fluxes can enhance the photoluminescence intensity of phosphor particles, that can be attributed both to the improvement of crystallization processes of YAG and to the stabilization of trivalence cerium ion in YAG：Ce^3 ＋.

Relationship between Multi-Phase Formation and Molecular Structure for Liquid Crystal System

4 mechanical model of liquid crystals （ LCs ） was used to explain the phase formation and thermal properties . The LC plusses in the model are micro- machine systems consisting of an ensemble of molecular rotors, and some dynamie parameters in a semi-experiment molecular orbit method. A novel explanation on the multi-phase formation of LC system is obtained. It is found that the value of the critical rotational velueity is a key parameter for the characterization of each homologous series. The dipole moment of the molecules was also discussed.

CRYSTALLISATION KINETICS AND PHASE TRANSFORMATION BEHAVIOUR OF ELECTROLESS NICKEL-PHOSPHORUS DEPOSIT WITH 6-9wt% PHOSPHORUS CONTENT

Crystallisation kinetic and phase transformation behaviour of the electroless nickel-phosphorus deposit with 6-9wt% phosphorus content were studied. The deposit was heated in the differential scanning calorimetry (DSC) apparatus to 300℃-800℃ at 20℃/min, followed by the X-ray diffraction (XRD) analysis. The sequence of crystallisation process was: mixture of amorphous and microcrystalline nickel phases → intermediate metastable, f. c. c. nickel and stable N13P phases → f. c. c. nickel and stable Ni3P phases. Preferred orientation of nickel {200} plane was developed after the heating processes. Activation energy of crystallisation process was determined from the DSC analyses at 5-50℃/min. Crystallisation temperatures were found increased with increasing heating rate.

Mechanical model study of relationship of molecular configuration and multiphase in liquid crystal materials

A mechanical model of liquid crystals （LCs） is applied to study the polymorphism of homologous series of terphenyl compounds. With a senti-experimental molecular orbit method, we calculate the moment of inertia which represents the rotation state to describe the phase transition temperature obtained from experimental data. We propose a novel explanation of the phase sequence or polymorphism of LC materials using the two key parameters, the moment of inertia and critical rotational velocity. The effect of molecular polarity on the appearance of liquid crystalline is also discussed.

Effects of Ru on the microstructure and phase stability of a single crystal superalloy

Two experimental single crystal superalloys, the Ru-free alloy and the Ru-containing alloy with [001 ] orientation, were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Ru on the microstructure and phase stability of the single crystal superalloy were investigated, y＇ directional coarsening and rafting were observed in the Ru-free alloy and Ru-containing alloy after long-term aging at 1070~C for 800 h. Needle-shaped o topologically close packed （TCP） phases precipitated and grew along the fixed direction in both the alloys. The precipitating rate and volume fraction of TCP phases decreased significantly by adding Ru. The compositions ofy and y＇ phases measured using an energy-dispersive X-ray spectroscope （EDS） in transmission electron microscopy （TEM） analysis showed that the addition of Ru lessened the partition ratio of TCP forming elements, Re, W and Mo, and decreased the satu- ration degrees of these elements in y phase, which can enable the Ru-containing alloy to be more resistant to the formation of TCP phases. It is indicated that the addition of Ru to the Ni-based single crystal superalloy with high content of the refractory alloying element can enhance phase stability.

Morphological evolution and growth kinetics of Kirkendall voids in binary alloy system during deformation process-Phase field crystal simulation study

The formation and growth of Kirkendall voids in a binary alloy system during deformation process were investigated byphase field crystal model.The simulation results show that Kirkendall voids nucleate preferentially at the interface,and the averagesize of the voids increases with both the time and strain rate.There is an obvious coalescence of the voids at a large strain rate whenthe deformation is applied along the interface under both constant and cyclic strain rate conditions.For the cyclic strain rate appliedalong the interface,the growth exponent of Kirkendall voids increases with increasing the strain rate when the strain rate is largerthan1.0×10-6,while it increases initially and then decreases when the strain rate is smaller than9.0×10?7.The growth exponent ofKirkendall voids increases initially and then decreases gradually with increasing the length of cyclic period under a square-waveform constant strain rate.

Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization

In this paper,we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals.Two groups of lasing peaks,of which the full widith at half maximum is about 0.3 nm,are clearly observed.The shorter-and longer-wavelength modes are associated with the excitation of the single laser dye（DCM） monomers and dimers respectively.The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light.When the polarization of the pump light is rotated from 0？to 90？,the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases.In addition,a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed.

Electrically tunable holographic polymer templated blue phase liquid crystal grating

In this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer tem- plated blue phase liquid crystal grating. This grating is obtained by preforming a polymer template comprised of periodic fringes, and then refilling it with a blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, our grating can remarkably reduce its switching voltage from 200 V to 43 V while maintaining a sub-millisecond response time. The holographic polymer templated blue phase liquid crystal （HPTBPLC） grating is free from electrode patterning, thus leading to a lower cost and more flexible applications.