Effect of Sr modification on microstructure and thermal conductivity of hypoeutectic Al−Si alloys

Trace amount of Sr(0.05 wt.%)was added into the hypoeutectic Al−Si(3−12 wt.%Si)alloys to modify their microstructure and improve thermal conductivity.The results showed that the thermal conductivity of hypoeutectic Al−Si alloys was improved by Sr modification,and the increment and increasing rate of the thermal conductivity gradually increased with Si content increasing.The improvement of thermal conductivity was primarily related to the morphology variation of eutectic Si phases.In Sr-modified Al−Si alloys,the morphology of eutectic Si phases was a mixed morphology of fiber structure and fine flaky structure,and the proportion of the fine flaky eutectic Si phases gradually decreased with Si content increasing.Under the Si content reaching 9 wt.%,the proportion of fine flaky eutectic Si phases was nearly negligible in Sr-modified alloys.Correspondingly,the increment and increasing rate of thermal conductivity of Sr-modified alloys reached the maximum and tended to be stable.

Grain refinement of Mg−Al binary alloys inoculated by in-situ oxidation

Utilizing oxide inclusion to induce heterogeneous nucleation event is an available method to achieve grain refinement.In this study,Mg−Al binary alloys were refined by inoculation of in-situ oxidation process.Results show that MgO and MgAl_(2)O_(4) phases are primary oxide products for Mg−xAl alloys inoculated by in-situ oxidation.For pure Mg and Mg−1Al alloy,MgO is the only oxide product.MgAl_(2)O_(4) is another oxide product for Mg−xAl alloy as Al content increases to 3 wt.%.For Mg−3Al alloy,average grain size significantly decreases from 1135 to 237μm,with a high grain refining ratio of 79.1%.Both MgO and MgAl_(2)O_(4) possess nucleating potency forα-Mg grain.MgAl_(2)O_(4) exhibits a higher nucleating potency due to the lower misfit withα-Mg.The grain refinement of Mg−xAl alloys inoculated by in-situ oxidation process is attributed to heterogeneous nucleation events ofα-Mg grains on MgO or MgAl_(2)O_(4) particles.

Design and preparation of Al-Fe-Ce ternary aluminum alloys with high thermal conductivity

Ce element was introduced to modify Al−2%Fe(mass fraction)binary alloy.The microstructures,crystallization behavior,electrical/thermal conductivities and mechanical properties of these alloys were systematically investigated.The results indicated that the appropriate Ce addition decreased the recalescence temperature and growth temperature of Al−Fe eutectic structure,improved the morphology and distribution of Fe-containing phase,and simultaneously increased the conductivity and mechanical properties.The annealed treatment improved the thermal conductivity of these alloys due to the decreasing concentration of point defects.Rolling process further broke up the coarser Fe-containing phases into finer particles and made the secondary phases uniformly distributed in theα(Al)matrix.After subsequent annealing treatment and rolling deformation,the thermal conductivity,ultimate tensile strength and hardness of the Al−2%Fe−0.3%Ce(mass fraction)alloy reached 226 W/(m·K),(182±1.4)MPa and HBW(49.5±1.7),respectively.

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.

Assessment of solidification characteristics of carbon-inoculated Mg-3%Al melt by thermal analysis

The Mg-3%Al melt was inoculated by carbon with different holding time.The effect of holding time on grain refining efficiency was evaluated.The solidification characteristics of the carbon-inoculated Mg-3%Al melt with different holding time were assessed by computer-aided cooling curve analysis.The results showed that Mg-3%Al alloy could be effectively refined by carbon inoculation.Slight fading phenomenon occurred with increasing the holding time to 60 min.Carbon inoculation could significantly influence the shape of cooling curves of Mg-3%Al melt.The nucleation starting and minimum temperatures increased.The recalescence undercooling and duration decreased to almost zero after carbon inoculation.The grain refining efficiency of carbon inoculation could be assessed by the shape of the cooling curve and solidification characteristic parameters including nucleation starting and minimum temperatures,recalescence undercooling and duration.

New Insights into Folding Kinetics of α,ω Dye-Functionalized Poly(N-isopropylacrylamide)

Two narrowly-distributed poly(N-isopropylacrylamide)(PNIPAM) samples were prepared via atom transfer radical polymerization (ATRP) with a novel dansyl functionalized initiator. The other end of the PNIPAM was functionalized by dabcyl group via click reaction. From the static fluorescence measurements, the fluorescence intensity of dansyl group and energy transfer efficiency between dansyl and dabcyl groups increased when the temperature increased from 36 °C to 45 °C, indicating that the microenvironment surrounding dansyl became hydrophobic and the distance between dansyl and dabcyl decreased. The kinetics of the conformational change of the dye-labeled PNIPAM was studied by a home-made laser-induced temperature jump device with fluorescent measurement. Our results revealed that the characteristic transition time was 3.8 and 5.8 ms for PNIPAM with degrees of polymerization of 85 and 142, respectively, indicating that the characteristic transition time was related to the chain length. Besides, characteristic transition time for the change of the energy transfer efficiency was 2.9 ms for PNIPAM with the degree of polymerization of 85, suggesting that the energy transfer efficiency change was faster than the fluorescence intensity change of dansyl group.

Construction of Type I Aggregation-Induced Emission Photosensitizers for Photodynamic Therapy via Photoinduced Electron Transfer Mechanism

Photodynamic therapy(PDT)as a non-invasive anticancer modality has received increasing attention due to its advantages of noninvasiveness,high temporospatial selectivity,simple and controllable operation,etc.PDT mainly relies on the generation of toxic reactive oxygen species(ROS)by photosensitizers(PSs)under the light irradiation to cause cancer cell apoptosis and death.However,solid tumors usually exhibit an inherent hypoxic microenvironment,which greatly limits the PDT efficacy of these high oxygen-dependent conventional type II PSs.Therefore,it is of great importance to design and develop efficient type I PSs that are less oxygen-dependent for the treatment of hypoxic tumors.Herein,a new strategy for the preparation of efficient type I PSs by introducing the photoinduced electron transfer(PET)mechanism is reported.DR-NO_(2) is obtained by introducing 4-nitrobenzyl to(Z)-2-(5-(4-(diethylamino)-2-hydroxybenzylidene)-4-oxo-3-phenylthiazolidin-2-ylidene)malononitrile(DR-OH)with aggregation-induced emission(AIE)feature.The AIE feature ensures their high ROS generation efficiency in aggregate,and the PET process leads to fluorescence quenching of DR-NO_(2) to promote triplet state formation,which also promotes intramolecular charge separation and electron transfer that is conducive for type I ROS particularly superoxide radicals generation.In addition,DR-NO_(2) nanoparticles are prepared by nanoprecipitation to possess nanoscaled sizes,high cancer cell uptake,and excellent type I ROS generation ability,which results in an excellent performance in PDT ablation of MCF-7 cancer cells.This PET strategy for the development of type I PSs possesses great potential for PDT applications against hypoxic tumors.

高分子网络凝胶法合成β-磷酸三钙粉体

采用高分子网络凝胶法合成β-磷酸三钙(βTCP)粉体,探讨了钙离子浓度、单体和交联剂用量和热处理温度等对粉体形貌、物相和粒径的影响。结果表明:当钙离子浓度为0.30 mol/L、单体和交联剂质量分数分别为6.0%和1.0%、热处理温度为950℃时,可得到结晶度高、粒径均匀、D90=3.58μm的类球形β-TCP粉体。