Highly thermally conductive POSS-g-SiCp/UHMWPE composites with excellent dielectric properties and thermal stabilities

Polyhedral oligomeric silsesquioxane grafting thermally conductive silicon carbide particle (POSS-g-SiCp) fillers, are performed to fabricate highly thermally conductive ultra high molecular weight polyethylene (UHMWPE) composites combining with optimal dielectric properties and excellent thermal stabilities, via mechanical ball milling followed by hot-pressing method. The POSS-g-SiCp/UHMWPE composite with 40 wt% POSS-g-SiCp exhibits relative higher thermal conductivity, lower dielectric constant and more excellent thermal stability, the corresponding thermally conductive coefficient of 1.135 W/mK, the dielectric constant of 3.22, and the 5 wt% thermal weight loss temperature of 423 °C, which holds potential for packaging and thermal management in microelectronic devices. Agari’s semi-empirical model fitting reveals POSS-g-SiCp fillers have strong ability to form continuous thermally conductive networks.     

Impact of defects on exciton diffusion in organic light-emitting diodes

The impact of defect concentration and current density on the effective singlet exciton diffusion length in 4’-bis(carbazol-9-yl)biphenyl (CBP) is quantified by analyzing the electroluminescent characteristics of several sets of OLEDs. The defect concentration and effective diffusion length are determined through fitting of the defect and CBP emission bands in the electroluminescence spectra under constant current operation using an analytical model derived based on the competition between exciton diffusion and energy transfer to defects. Defect concentrations of 3 ± 1 × 10¹⁸ cm⁻³, 2 ± 1 × 10¹⁸ cm⁻³ and 0.3 ± 0.7 × 10¹⁸ cm⁻³ are calculated in three sets of OLEDs, in which the effective diffusion length decreases as the defect concentration increases. Modelling the dependence of the effective diffusion length on defect concentration a “defect free” diffusion length of 4.5 ± 0.3 nm is obtained for CBP singlet excitons in these devices operated under low current density. We also show that the driving voltage scales linearly with the defect concentration.     

Interfacial structure of steel–aluminum bonding plate under non-equilibrium rapid solidification

A steel–aluminum solid–liquid bonding plate is prepared using a non-equilibrium rapid solidification method (including four kinds of processes such as roughening the steel plate surface, immersing in flux at the steel plate surface, short-time bonding and rapid solidification). The interfacial structure of the bonding plate is investigated by means of electron probe microanalysis and X-ray diffraction. The results show that the interfacial structure of the bonding plate under non-equilibrium rapid solidification is quite different from that of the bonding plate in conventional steel–aluminum solid–liquid bonding, i.e. the interface of the bonding plate under non-equilibrium rapid solidification is made up of an aluminum-rich region (in the form of a group of Fe₄Al₁₃ teeth that grow from the contact surface to the steel side) at the bulge of steel plate surface and an aluminum-poor region (in the form of Fe–Al solid solution of which the Al content is less than 3.5 wt%) at the concave surface of the steel plate alternately.     

Effect of consolidation and oxide dispersoid addition on phase formation and mechanical properties of WTi ODS alloy

WTi alloys are presently considered promising candidates for plasma facing components in advanced nuclear energy systems. The mechanically alloyed WTi model alloys consolidated by different techniques were investigated. The effect of different amounts of the dispersed oxide particles on characteristics and properties of the WTi materials was also discussed. The results show that a homogeneous fine grain structure without formation of Ti-rich oxides is obtained in the model alloy sintered by spark plasma sintering. The (W,Ti)C solid solution and α″-Ti martensite phase are also found in the alloy confirmed by TEM investigation, which can be contributed to the effect of the carbon contamination and cooling rate during the process. In this work, it is clear to demonstrate that the presence of different carbides and Ti phases plays an important role in determining hardness and elastic modulus of the materials. The microstructure homogeneity and mechanical properties of the alloys can be further improved by increasing numbers of oxide dispersoids.     

Synthesis and properties of cinnamic acid series organic UV ray absorbents–interleaved layered double hydroxides

Organic ultraviolet (UV) ray absorbents, cinnamic acid (CA) and p-methoxycinnamic acid (PMOCA) were intercalated into Zn₂Al layered double hydroxides (Zn₂Al-LDHs) by co-precipitation reaction. The organic–inorganic nanocomposites, Zn₂Al-LDH/CA and Zn₂Al-LDH/PMOCA were obtained. The samples showed excellent UV ray absorption ability and their catalytic activity for the air oxidation of castor oil greatly decreased when the organic UV ray absorbents were intercalated in the layers of the Zn₂Al-LDHs. The studies suggested that Zn₂Al-LDH/organic UV absorbent nanocomposites might be used as safe sunscreen materials.     

氧化铝泡沫陶瓷及其表面溶胶–凝胶涂层的制备

采用有机泡沫浸渍法制备了氧化铝泡沫陶瓷,考察了工艺参数对泡沫陶瓷结构和性能的影响,研究了溶胶–凝胶法在泡沫陶瓷表面形成凝胶涂层的制备工艺。结果表明：对有机泡沫进行15%NaOH水溶液处理及5%PVA水溶液活化处理,采用离心挂浆工艺,制备了3种规格的的泡沫陶瓷,其孔尺寸范围为0.8～1.2mm,孔筋尺寸为0.1～0.25mm。泡沫陶瓷的抗压强度随ppi值（每英寸模板孔数）的增大而提高;二次挂浆有利于抗压强度的提高。泡沫陶瓷的抗热震性能随ppi值的减小而增加。采用负压浸胶工艺,可较好地在泡沫陶瓷表面形成TiO2凝胶涂层。     

Wetting and pressureless infiltration in the CuTi/Al2O3 system under poor vacuum

Work is aimed at preparation of Cu/Al₂O₃ composite by pressureless metal infiltration of porous alumina with simple vacuum equipment. Improvement of wetting by addition of Ti to Cu is investigated in sessile drop tests with various geometrical configurations in vacuum of 1–10 Pa. The results showed that a pre-alloyed Cu did not wet alumina substrate while stacked Cu and Ti blocks did, even though the latter had the same nominal alloy content (Ti: 10 wt%). This result had been proved by a following pressureless infiltration test, i.e. a CuTi/Al₂O₃ composite was formed with stacked Cu and Ti blocks at 1300 °C. Wettability, interfacial chemistry and microstructure were discussed with the aid of SEM and EDAX analysis in the paper. It was suggested that the initial reactant, which benefits the wettability, could be evolved to the one with a higher O:Ti ratio due to poor vacuum condition, higher temperature and longer holding time.     

Photocatalytic overall water splitting by Z-scheme g-C3N4/BiFeO3 heterojunction

Solar water splitting by photocatalysis in the absence of sacrificial agent has been identified as a promising approach to produce green hydrogen. Increasing photocatalytic efficiency is the core issue in this process. Forming heterojunctions is one potential solution to improve photoactivity. Herein, we successfully synthesized several g-C₃N₄/BiFeO₃ composites containing different mass ratio of g-C₃N₄ by an uncomplicated and cost-effective method. The composite samples exhibited remarkably enhanced photocatalytic performance compared with the bare BiFeO₃ and g-C₃N₄. The highest hydrogen production rate obtained is ~ 160.75 μmol h⁻¹.g-¹ under UV irradiation and ~23.31 μmol h⁻¹.g-¹ under visible light irradiation. This enhanced photocatalytic activity is attributed to the synergistic effect of the junction and Z-scheme charge transfer mechanism between BiFeO₃ and g-C₃N₄, which can effectively accelerate the separation of photogenerated electron-hole pairs and also capability of carrying out redox reaction.     

化学镀铜对氧化铝陶瓷和高铬铸铁之间润湿性的影响

采用化学镀铜的方法,在氧化铝陶瓷表面进行镀铜处理,以期改善金属液与陶瓷之间的润湿性,测量润湿性采用座滴法模型.结果证明,在热应力的作用下,陶瓷易受其影响而破碎;与未经表面涂层处理的Al2O3陶瓷相比,镀铜后的陶瓷与金属液之间的润湿性更好.     

Effect of environmental conditions on the properties of fresh and hardened concrete

The effect of varying environmental conditions, at the time of casting on the properties of fresh and hardened concrete was evaluated. The influence of air temperature, wind velocity, and relative humidity on plastic shrinkage, compressive strength, pulse velocity and pore structure of concrete was investigated. Results indicate that exposure conditions at the time of casting significantly affect plastic shrinkage of concrete. As expected elevated temperature affected porosity, compressive strength, and pulse velocity of concrete. Casting of concrete at elevated temperature decreased its compressive strength. Similarly, the pulse velocity of concrete cast at 45°C was less than that of cast at 30°C. The volume of total pores in the concrete specimens cast at 45°C was more than that of cast at 30°C. The lower pulse velocity and increased pore volume in the concrete cast at 45°C than that cast at 30°C may be attributed to the coarse pore structure formed in the former than the latter. Other weather parameters, such as relative humidity and wind velocity, also influence the properties of fresh and hardened concrete.