Preparation and investigation of the combustion behavior of polypropylene/organomodified MgAl-LDH micro-nanocomposite

Layered double hydroxides (LDHs) are considered as a new emerging class of clays and they have a promising future in the field of nanocomposites due to their highly tunable properties. In this research, polypropylene/organomodified magnesium-aluminum LDH (PP/O-MgAl-LDH) composites were prepared by direct melt compounding. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the samples. Both XRD and TEM images of the composites illustrate the formation of a mixed morphology of micro and nano scale dispersion of MgAl-LDH in the matrix. Its combustion behaviors were examined via microscale combustion calorimeter (MCC), and char residues investigated by SEM. The MCC results show that the addition of Mg-Al-LDH into PP can efficiently decrease the specific heat release rate (HRR), the heat release capacity (HRC), and total heat release (THR), indicating the flame retardancy of the composite are improved. Flame retardant properties of PP/O-MgAl-LDH micro-nanocomposite were further enhanced with the increasing amounts of MgAl-LDH concentration.     

Microstructure and strength of B2-ordered (Ni,Co)Al

A transmission electron microscopy (TEM) investigation of the morphologies and crystal structures of precipitates in supersaturated B2-ordered (Ni,Co)Al has revealed that rod-like precipitates of the (Ni,Co)₂Al phase with a hexagonal structure form parallel to the <111> direction of the B2 matrix. By aging at temperatures below 973 K, a long period superlattice structure of hexagonal (Ni,Co)₂Al was formed. The (Ni,Co)Al hardens appreciably by the precipitation of these phases. An energy dispersive spectroscopy (EDS) was used to analyze the compositions of each phase formed in the B2-(Ni,Co)Al. The effects of the dispersion of the (Ni,Co)₂Al phase on the temperature dependence of the strength of the B2-(Ni,Co)Al have been investigated over a temperature range from 298 K to 1173 K.     

Controlling friction and wear of nc-WC/a-C(Al) nanocomposite coating by lubricant/additive synergies

Owing to increasing demands for reductions in emissions and improvements in fuel economy in the automotive industry, there is an urgent need to improve tribological performances of components. In the current paper, an nc-WC/a-C(Al) carbon-based nanocomposite coating was fabricated successfully via the magnetron sputtering process. The microstructure and mechanical properties of the as-fabricated nanocomposite coating were investigated. In particular, its friction and wear behaviors under poly-alpha-olefin oil lubricant added with anti-wear (AW), extreme-pressure (EP), or molybdenum dialkyldithiocarbamate (MoDTC) additive were systemically evaluated. Results show that the nc-WC/a-C(Al) nanocomposite coating has a typical nanocrystallite/amorphous microstructure and good mechanical properties. The significant improvement in the tribological performance of the boundary-lubricated nc-WC/a-C(Al) coating is mainly attributed to the WS₂ or MoS₂ + WS₂-containing tribofilm when S-based EP or MoDTC additive was used. Superior tribological performance of nc-WC/a-C(Al) nanocomposite coating was achieved by lubricant/additive synergies, indicating its potential application as a protective coating for automotive tribo-components.     

Li(Mn1/3Ni1/3Co1/3)1-yMyO2(M=Al,Mg,Ti)正极材料的制备及性能

采用液相共沉淀合成锰镍钴氢氧化物前驱体, 在前驱体中掺入元素M(M=Al, Mg, Ti), 与锂结合生成Li(Mn1/3Ni1/3Co1/3)0.98M0.02O2材料, 结果表明掺杂可有效提高材料的循环性能. X射线衍射结果表明 随掺钛量增大(0≤y≤0.15), 晶格畸变增大, 半高宽变大, 晶粒粒径增大; 其中掺钛量y=0.1的材料电化学性能表现最好, 以20 mA/g电流充放电, 在2.5～4.6 V电压区首次放电容量可达215 mA·h/g.     

Synthesis and characterization of layered Li（Ni1/3Mn1/3CO1/3）O2 cathode materials by spray-drying method

Spherical Li(Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 was prepared via the homogenous precursors produced by solution spray-drying method. The precursors were sintered at different temperatures between 600 and 1 000 ℃ for 10 h. The impacts of different sintering temperatures on the structure and electrochemical performances of Li(Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 were compared by means of X-ray diffractometry(XRD), scanning electron microscopy(SEM), and charge/discharge test as cathode materials for lithium ion batteries. The experimental results show that the spherical morphology of the spray-dried powers maintains during the subsequent heat treatment and the specific capacity increases with rising sintering temperature. When the sintering temperature rises up to 900 ℃ , Li(Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 attains a reversible capacity of 153 mA·h/g between 3.00 and 4.35 V at 0.2C rate with excellent cyclability.     

Interfacial reactions between Sn-2.5Ag-2.0Ni solder and electroless Ni(P) deposited on SiCp/Al composites

A novel Sn-2.5Ag-2.0Ni alloy was used for soldering SiCp/Al composites substrate deposited with electroless Ni(5%P) (mass fraction) and Ni(10%P) (mass fraction) layers. It is observed that variation of P contents in the electroless Ni(P) layer results in different types of microstructures of SnAgNi/Ni(P) solder joint. The morphology of Ni3Sn4 intermetallic compounds (IMCs) formed between the solder and Ni(10%P) layer is observed to be needle-like and this shape provides high speed diffusion channels for Ni to diffuse into solder that culminates in high growth rate of Ni3Sn4. The diffusion of Ni into solder furthermore results in the formation of Kirkendall voids at the interface of Ni(P) layer and SiCp/Al composites substrate. It is observed that solder reliability is degraded by the formation of Ni2SnP, P rich Ni layer and Kirkendall voids. The compact Ni3Sn4 IMC layer in Ni(5%P) solder joint prevents Ni element from diffusing into solder, resulting in a low growth rate of Ni3Sn4 layer. Meanwhile, the formation of Ni2SnP that significantly affects the reliability of solder joints is suppressed by the low P content Ni(5%P) layer. Thus, shear strength of Ni(5%P) solder joint is concluded to be higher than that of Ni(10%P) solder joint. Growth of Ni3Sn4 IMC layer and formation of crack are accounted to be the major sources of the failure of Ni(5%P) solder joint.     

原位合成(Al_2O_3+Al_3Ti)_P/Al复合材料的制备研究

通过对Al-TiO_2-SiO_2体系混合粉末固-液原位合成制备出了(Al_2O_3+Al_3Ti)_P/Al复合材料.利用X射线衍射仪、扫描电镜等方法观察分析了其物相和显微组织形貌.结果表明:原位反应制备的(Al_2O_3+Al_3Ti)_P/Al复合材料,金属间化合物增强相Al_3Ti均匀分布于基体,陶瓷相Al_2O_3颗粒非常细小,弥散分布于基体中,使材料的硬度等性能得到提高.     

Sintering densification and properties of Al2O3／PSZ （3Y） ceramic composites

1　INTRODUCTIONAl2 O3ceramicsisoneofthewide spreadingma terialsbecauseitholdsgoodfeaturessuchasresistancetohightemperature ,oxidation ,corrosionandabra sion .However ,thebrittlenatureofAl2 O3ceramicshaspromptedustoexploreavarietyofapproachestoenhanceitsfracturetoughness .SinceGarvieetal[1]advancedatheoryin 1975 ,thatistoimprovethefracturetoughnessandflexuralstrengthofZrO2 ce ramicswithmartensitictransformation ,ZrO2 hasbeenreceivingconsiderableattention .AddingMgO ,CaO ,Y2 O3andCeO2…     

Processing, microstructure, and properties of laser remelted Al2O3/Y3Al5O12（YAG） eutectic in situ composite

Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12（YAG） eutectic in situ composite. The microstructure characteristic and solidification behavior were studied using scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）, X-ray diffractometry（XRD） and simultaneous thermal analysis（STA）. The hardness and fracture toughness were obtained using an indentation technique. The results show that the laser remelted Al2O3/YAG composite has a homogeneous eutectic microstructure without microcrack and pore. The component phases of Al2O3 and YAG are three-dimensionally and continuously reticular connected, and finely coupled without grain boundaries, colonies and amorphous phases between interfaces. The eutectic interspacing is greatly refined with increasing the scanning rate and average is only l μm. The synthetically thermal analysis indicates that the eutectic temperature of Al2O3-YAG is 1 824 ℃, well matching the phase diagram of Al2O3-Y2O3 system. The maximum hardness reaches 19.5 GPa and the room fracture toughness is 3.6 MPa.m^1/2.