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Effects of phase transition temperature and preheating on residual stress in multi-pass & multi-layer laser metal deposition
摘要： To investigate the influences of phase transition temperature and preheating on the residual stress of multi-layer and multi-pass laser metal deposition (LMD), the multi-layer and multi-pass LMD, with and without preheating, were performed using five kinds of alloy with different phase transition features, and their residual stresses were measured using the hole drilling method. A finite-element (FE) model incorporating the phase transition was developed based on experimentally obtained physical property data. The results demonstrated that the low-temperature solid phase transition has a tensile stress relaxation effect, which leads to the formation of a compressive stress area. This relaxation effect was observed to decrease with the increase of the phase transition temperature. The high-temperature solid phase transition has no significant tensile stress relaxation effect during the multi-layer and multi-pass LMD process, which is different from the single track LMD. when the solid phase transition temperature is low, the preheating can improve the uniformity of the stress field only to a certain extent. However, when the preheating increases the lowest temperature of the thermal cycle and makes it higher than the starting point temperature of the solid phase transition, the tensile stress relaxation effect of the solid phase transition can be brought into full play.
关键词： Finite element analysis,Preheating,phase transition temperature,Residual stress,Laser metal deposition
更新于2025-11-28 14:24:20
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Molecular dynamics simulation study on the structure and properties of polyimide/silica hybrid materials
摘要： A type of polyimide/silica (PI/SiO2) copolymer model was established through the dehydration of tetraethyl orthosilicate molecules (TEOS) and bonding to a silane coupling agent. The content of SiO2 was controlled by adjusting the number of molecules which bound to the TEOS. Finally, the silica was formed into a hybrid model (hybrid PI/SiO2) with a small molecule embedded in the PI. The model was optimized by geometric and molecular dynamics and the changes in the model structure, Young’s modulus, shear modulus, and glass-transition temperature (Tg) were analyzed. The results showed that the density and cohesive energy density of the composites could be improved by doping SiO2 in PI. Young’s modulus and shear modulus of PI/SiO2 hybrid materials were higher than undoped PI. The tensile strength reached 568.15 MPa when the doping content was 9%. Therefore, the structure design and content control of SiO2 was an effective way to improve the performance of a PI/SiO2 composite. The variation of Tg and tensile strength of PI/SiO2 hybrid composites is consistent with that of PI/SiO2 composite synthesized in real experiment, which will be a convenient method for new material design and performance prediction. ? 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 136, 47335.
关键词： molecular dynamics,shear modulus,Young’s modulus,polyimide/silica,glass-transition temperature
更新于2025-09-23 15:23:52
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Facile synthesis of thermal responsive fluorescent poly(imino ether sulfone): Nondestructive detection of Tg and erasable thermal imaging
摘要： A novel heat-resistant fluorescent polymer poly(imino ether sulfone) (PIES) as thermally erasable and writable imaging material has been synthesized via a facile nucleophilic substitution polycondensation reaction. Taking advantage of the tenability of the 'push-pull' π-electron mode by changing temperatures, the Tg of PIES film can be 'naked eye' nondestructively detected by taking advantage of the visual fluorescence quenching.
关键词： Nondestructive detection,Poly(imino ether sulfone),High performance polymer,Glass transition temperature
更新于2025-09-23 15:23:52
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Assessing Physical Stability of Colloidal Dispersions Using Turbiscan Optical Analyzer
摘要： The physical stability of aqueous colloidal dispersions containing highly concentrated droplets of poorly water-soluble drugs has recently been identified as one of the main considerations in developing amorphous solid dispersions (ASDs). Turbiscan, an instrument based on multiple light scattering technology, was employed for the first time to assess colloidal dispersions with ritonavir as the model compound. The physical instability of ritonavir-rich droplets was monitored directly with and without the presence of candidate polymer additives at different drug concentrations and temperatures. The mechanism of the observed instability was confirmed to be coalescence of liquid droplets, based on the low glass transition temperature of water-saturated amorphous ritonavir determined using a newly developed experimental procedure. Temperature and solvent composition, within the range studied, have little influence on the kinetics of ritonavir coalescence. On the contrary, higher concentration of drug, i.e., more droplets per unit volume, greatly accelerates the coalescence process. In addition, polymers with varying degrees of hydrophobicity resulted in different levels of effectiveness in stabilization which is likely related to the strength of drug-polymer interactions and the corresponding differences in surface adsorption. This work demonstrates that the Turbiscan optical analyzer can be used as a rapid screening tool that provides a first-pass, high-throughput feasibility ranking of different excipients and additives to support the development of ASD formulations.
关键词： nanodroplets,coalescence,glass transition temperature,physical stability,stabilization,amorphous,ritonavir,colloidal dispersions,Turbiscan
更新于2025-09-23 15:22:29
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Optimized thermochromic properties of VO2/CoFe2O4 nanocomposite films via band gap engineering
摘要： VO2/CoFe2O4 nanoparticle composites were synthesized by hydrothermal method combined with annealing treatment. The nanocomposites consist of quasi-spherical nanoparticles with an average size of about 70 nm. The thermochromic properties of the nanocomposite films can be modulated by changing film thickness and the content of CoFe2O4 in the nanocomposites. The band gap of the VO2/CoFe2O4 nanocomposites increases with increasing CoFe2O4 additive content. The introduction of CoFe2O4 into VO2 matrix can not only lower the phase transition temperature, but also optimize the luminous transmittance and solar modulation ability of the VO2/CoFe2O4 nanocomposites as well. Our findings demonstrate a promising avenue in constructing VO2-based smart films with excellent thermochromic performance.
关键词： Solar modulation ability,VO2/CoFe2O4 nanocomposite,Luminous transmittance,Phase transition temperature
更新于2025-09-23 15:21:21
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Study of materials structure physics of isomorphic LiNbO <sub/>3</sub> and LiTaO <sub/>3</sub> ferroelectrics by synchrotron radiation X-ray diffraction
摘要： Electron charge density studies of stoichiometric LiNbO3 and LiTaO3 ferroelectrics have been carried out by analyzing the synchrotron radiation X-ray powder di?raction data using a combination of the Rietveld and maximum entropy methods. The clear relationships between the Nb(Ta)–O bond length, the electron charge density on the Nb(Ta)–O bond, and the phase transition temperature TC are revealed for isomorphic structures. Nb(Ta)–O bonding plays an important role in the elevation of TC. The TC in LiNbO3 being higher than that in LiTaO3 is attributed to the larger lattice distortion of the Nb–O oxygen octahedron in LiNbO3. The validity of estimating TC for LiNbO3 family crystals from the degree of lattice distortion in the ferroelectric structure is discussed.
关键词： ferroelectric,LiTaO3,X-ray diffraction,synchrotron radiation,LiNbO3,phase transition temperature,electron charge density
更新于2025-09-23 15:21:21
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Polarization-dependent phase transition temperature in plasmonic thin films
摘要： Nano-engineering the effective, macroscopic properties of composite materials is becoming increasingly important in material sciences and device development. Here, we report on using embedded plasmonic nanorods to modify the effective, as opposed to the intrinsic, phase transition temperature of vanadium oxide, a phase change material vital for infrared imaging and thermochromics. The nanorods function as controllable, nano-sized thermal sources through the excitation and dissipation of surface plasmons. The polarization dependence in the excitation efficiency modifies the effective phase transition temperature by up to 4.2 °C under broadband illumination of 5.0 W. This work constitutes a proof-of-principle demonstration of tunable and reversible plasmonic modulation of the phase transition temperature in a phase change material. It also represents a new strategy of thermo-plasmonic engineering at the nanoscale.
关键词： vanadium oxide,phase transition temperature,plasmonic thin films,thermo-plasmonic engineering
更新于2025-09-23 15:21:01
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The Phase Behavior in the Active Layer of Small Molecule Organic Photovoltaics: The State Diagram of p-DTS(FBTTh <sub/>2</sub> ) <sub/>2</sub> :PC <sub/>71</sub> BM
摘要： A comprehensive study was undertaken to obtain a more fundamental understanding of the phase behavior of the p-DTS(FBTTh2)2:PC71BM system, used in small molecule organic solar cells, with a strong focus on the amorphous phase and its influence on crystallinity. Three dedicated thermal protocols were used in combination with advanced thermal analysis, solid-state NMR, and wide angle X-ray diffraction. Rapid cooling, to avoid structure formation and gain insight in the amorphous phase, and slow cooling, to promote structure formation, were used as limiting cases to explain the intermediate behavior after device processing from solution. A complete state diagram was developed and the glass transition (Tg) - composition relationship was determined. In the case of slow cooling and the procedure used for device processing, the rapid crystallization of p-DTS(FBTTh2)2 leads to an enrichment of the amorphous phase in PC71BM, increasing its Tg and causing vitrification of the mixed amorphous phase before crystallization when the total amount of PC71BM exceeds 70 wt%. The common processing additive 1,8-diiodooctane (DIO) was found to lead to a lower p-DTS(FBTTh2)2 crystallinity and smaller average crystal size. More importantly, it acts as a strong plasticizer, lowering Tg significantly and thus reducing the morphological stability of the p-DTS(FBTTh2)2:PC71BM mixtures.
关键词： p-DTS(FBTTh2)2:PC71BM,glass transition temperature,wide angle X-ray diffraction,phase behavior,crystallinity,amorphous phase,small molecule organic photovoltaics,thermal analysis,solid-state NMR,1,8-diiodooctane (DIO)
更新于2025-09-23 15:19:57
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Effect of Zr Doping on the Magnetic and Phase Transition Properties of VO2 Powder
摘要： In this work, V1?xZrxO2 powder (x = 0, 0.01, 0.02, 0.04) was synthesized by two step hydrothermal method. The micro-topography, magnetic and phase transition properties have been investigated using various measurement techniques. All prepared V1?xZrxO2 powder samples exhibit monoclinic structure at room temperature. With the Zr4+ ions doping concentration increased, the shapes of VO2 particles change from spherical to rectangular slice. Besides, the saturation magnetic moment of the samples decrease with the increase of doped Zr4+ ions concentration, while their phase transition temperature increase gradually with Zr ions doping at a rate of around 2 ?C/at% on average. We investigated the Zr doping effects on V-V dimers and con?rmed the role of V-V dimers in phase transition. We speculate that more V-V dimers form with Zr doping by magnetic measurements, which result in the monoclinic phase of Zr-doped VO2 sample is more stable than rutile phase. Therefore the phase transition temperature is elevated by Zr doping in our experiment. We further consider that the VO2 phase transition should be ascribed to Peierls transition caused by the changing of V-V dimers.
关键词： V-V dimer,magnetic properties,Zr-doped,phase transition temperature
更新于2025-09-19 17:15:36
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Investigations of physical parameters of Ge doped binary Se-As chalcogenide glassy alloys for optical fiber application
摘要： Germanium doped chalcogenide glasses have potential applications in non- linear and optoelectronic devices. Ternary Ge-Se-As system has been considered to study the different important physical parameters. The impact of deviation of Ge on the cost of As in Ge-Se-As glassy system has been discussed in terms of average coordination number, cohesive energy, heat of atomization, and the theoretical optical band gap of the system. Almost all the physical parameters are found to change linearly with the variation in Ge content. The physical properties approximated in the present study can reveal the structural details for optical fibers.
关键词： Chalcogenide glasses,cohesive energy,mean bond energy,glass transition temperature,lone pair electrons
更新于2025-09-16 10:30:52