根管倒充填材料生物相容性和边缘密合性的研究

本文应用6种材料在离体牙根作根管倒充填并做细胞附着实验,通过电镜摄片作材料密合度的测定和细胞附着情况的观察,以比较和筛选理想的倒充填材料。实验结果指出:玻璃离子体粘固粉具有良好的生物相容性和良好的边缘密合性。国产玻璃离子体粘固粉的性能与日本产的性能无大差别,可作为首选的根管倒充填材料。银汞合金密合性不仅比玻璃离子体粘固粉差,甚至不如磷酸锌粘固粉,生物相容性也不及玻璃离子体粘固粉。

Microstructure and mechanical properties of aluminium metal matrix composites with addition of bamboo leaf ash by stir casting method

Al-4.5%Cu alloy was used as a matrix at2%,4%and6%of bamboo leaf ash(BLA)which was extruded from agro waste and was used as reinforcement.The composite which was fabricated by stir casting method possessed superior properties due to an effective bonding between matrix and reinforcement particles.The fabricated composite specimens were subjected to various tests to determine the mechanical properties such as density,porosity,hardness and tensile strength.The results were compared with basic matrix alloy.Furthermore,the OM,SEM with EDAX and XRD analyses were carried out to analyze the dispersion of the reinforced particles in the selected matrix alloy.It was observed that the homogeneous distribution of BLA particles in composites was intragranular in nature.Moreover,it was also observed that BLA particles were well bonded with matrix alloy with clear interface.It was also found that the density decreased with increase in mass fraction of BLA particles and porosity increased with increase in mass fraction of BLA particles.The hardness and tensile strength were increased up to4%of BLA in the composite,with a further increase in BLA content the hardness and tensile strength decreased.

The Effect of Ionizing Radiation and Magnetic Field on Deformation Properties of High Density PolyethylenelAcrylonitrile-Butadiene Composites

The effect of magnetic field and ionizing radiation on the mechanical properties of polymer blends consisting of high density polyethylene （HDPE） and acrylonitrile-butadiene rubber （NBR） has been investigated. The purpose of the work was to create HDPE/NBR blend composites of significantly different compositions （with an excess of HDPE, intermediate ones, and with an excess of NBR） and to investigate the role of composition on mechanical deformation properties under the influence of magnetic field. The investigation has importance from the engineering viewpoint, since thermoplastic composite materials have been used as structural elements in thermonuclear and engineering fields, like wires, insulation materials and others, which are frequently subjected to mechanical loadings under the effect of magnetic field greater than 1 T. One part of the blends has been irradiated with 5 MeV accelerated electrons up to absorbed dose D equal to 150 kGy. Unirradiated and the radiation modified blends have been exposed to a constant magnetic field with induction B equal to 1.0 T, 1.5 T and 1.7 T. It is found that the action of magnetic field decreases the elastic modulus of unirradiated materials. Decrement of elastic modulus is reduced with increase of the content of NBR in composites. It is also found that preliminary irradiation noticeably decreases the effect of magnetic field. Data of the influence of the magnetic field, radiation cross-linking, and the ratio of the components on the creep are also obtained.

Si_3N_4/Ni nanocomposite formed by electroplating: Effect of average size of nanoparticulates

Properties of Si3N4/Ni electroplated nanocomposite such as corrosion current density after long time immersion,roughness of obtained layer and distribution of nanometric particulates were studied.Other effective factors for fabrication of nanocomposite coatings were fixed for better studying the effect of the average size of nanoparticulates.The effects of the different average size of nanometric particulates(ASNP)from submicron scale(less than 1μm)to nanometric scale(less than 10 nm)were studied.The nanostructures of surfaces were examined by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and atomic force microscopy(AFM).Corrosion rates of the coatings were determined using the Tafel polarization test.It is seen that decreasing the ASNP will lead to lower corrosion current densities;however,in some cases,pitting phenomena are observed.The roughness illustrates a minimum level while the distribution of nanometric particulates is more uniform by decreasing the ASNP.The effects of pulsed current on electrodeposition(frequency,duty cycle)and concentration of nanoparticulates in electrodeposition bath on trend of obtained curves have been discussed.Response surface methodology was applied for optimizing the effective operating conditions of coatings.The levels studied were frequency range between 1 000 and 9 000 Hz,duty cycle between 10%and 90%and concentration of nanoparticulates of 10-90 g/L.

Design Details of Low-Energy and Passive Houses Using Composites from Waste Raw Materials

The article deals with potential use of waste materials in construction industry, specifically use of high density polyethylene （HDPE）. The article is focused in particular on recycled polyethylene application in products designed for construction industry, especially for passive houses. Currently certain building details of passive houses are not perfect or their solution results in higher economic demands related to house purchase and its further use. For the purpose of this thesis details of windows installation in external walls and elimination of thermal bridges in wall footing have been chosen. Products were subject to mathematic modelling of thermal technique and statics. The executed mathematic models documented that products are fully functional and that the suggested product successfully eliminate insufficiencies of some currently applied solutions.

Improved photoconductive properties of composite nanofibers based on aligned conjugated polymer and single-walled carbon nanotubes

We successfully address the challenge of aligning single-walled carbon nanotubes （SWNTs） and conjugated polymer chains in composite nanofibers for enhancing their opto-electrical properties. A pore-filling template strategy has been developed to prepare such nanocomposites from SWNTs and poly（para-phenylene vinylene） （PPV） chains, with both species well-oriented aligned along the pore axis. Addition of the SWNTs leads to a remarkable increase in photocurrent of four orders of magnitude as compared to equivalent pristine PPV nanofibers. Further analysis indicates that the strong photocurrent enhancement is not simply an effect of alignment, but additionally benefits from alignment-enhanced interaction of polymer chains with SWNTs, as supported by density functional theory （DFT） calculations.

Graphene-based Li-ion hybrid supercapacitors with ultrahigh performance

There is a growing demand for hybrid supercapacitor systems to overcome the energy density limitation of existing-generation electric double layer capacitors （EDLCs）, leading to next generation-Ⅱ supercapacitors with minimum sacrifice in power density and cycle life. Here, an advanced graphene-based hybrid system, consisting of a graphene-inserted Li4Ti5O12 （LTO） composite anode （G-LTO） and a three-dimensional porous graphene-sucrose cathode, has been fabricated for the purpose of combining both the benefits of Li-ion batteries （energy source） and supercapacitors （power source）. Graphene-based materials play a vital role in both electrodes in respect of the high performance of the hybrid supercapacitor. For example, compared with the theoretical capacity of 175 mA-h.g-1 for pure LTO, the G-LTO nanocomposite delivered excellent reversible capacities of 207, 190, and 176 mA·1h·g-1 at rates of 0.3, 0.5, and 1 C, respectively, in the potential range 1.0-2.5 V vs. Li/Li＋; these are among the highest values for LTO-based nano- composites at the same rates and potential range. Based on this, an optimized hybrid supercapacitor was fabricated following the standard industry procedure; this displayed an ultrahigh energy density of 95 Wh·kg-1 at a rate of 0.4 C （2.5 h） over a wide voltage range （0-3 V）, and still retained an energy density of 32 Wh·kg-1 at a high rate of up to 100 C, equivalent to a full discharge in 36 s, which is exceptionally fast for hybrid supercapacitors. The excellent performance of this Li-ion hybrid supercapacitor indicates that graphene-based materials may indeed play a significant role in next-generation supercapacitors with excellent electrochemical performance.

Self-assembled energetic coordination polymers based on multidentate pentazole cyclo-N_5^-

Coordination to form polymer is emerging as a new technology for modifying or enhancing the properties of the existed energetic substances in energetic materials area. In this work, guanidine cation CN3 H6+ (Gu) and 3-amino-1,2,4-triazole C2H4N4(ATz) were crystallized into NaN5 and two novel energetic coordination polymers(CPs),(NaN5)5[(CH6-N3)N5](N5)3–(1) and(NaN5)2(C2H4N4)(2) were prepared respectively via a self-assembly process. The crystal structure reveals the co-existence of the chelating pentazole anion and organic component in the solid state. In polymer 1, Na+and N5– were coordinated to form a cage structure in which guanidine cation [C(NH2)3]+ was trapped;for polymer 2, a mixedligand system was observed;N5 – and ATz coordinate separately with Na+and form two independent but interweaved nets. In this way, coordination polymer has been successfully utilized to modify specific properties of energetic materials through crystallization. Benefiting from the coordination and weak interactions, the decomposition temperatures of both polymers increase from 111°C(1D structure [Na(H2 O)(N5)]?2 H2 O) to 118.4 and 126.5°C respectively. Moreover, no crystallized H2 O was generated in products to afford the anhydrous compounds of pentazole salts with high heats of formation( >800 kJ mol–1). Compared to traditional energetic materials, the advantage in heats of formation is still obvious for the cyclo-N5– based CPs, which highlights cyclo-N5– as a promising energetic precursor for high energy density materials(HEDMs).

Active catalysts based on cobalt oxide@cobalt/N-C nanocomposites for oxygen reduction reaction in alkaline solutions

Over the past few years, electrocatalysis for the oxygen reduction reaction in alkaline solutions has undergone tremendous advances, and non-precious metal catalysts are of prime interest. In this study, we present a highly promising CoO@Co/N-C （where N-C represents a N-doped carbon material） catalyst, achieving an onset potential of 0.99 V （versus the reversible hydrogen electrode （RHE）） and a limiting current density of 7.07 mA-cm-2 （at 0.3 V versus RHE） at a rotation rate of 2,500 rpm in an O2-saturated 0.1 M KOH solution, comparable to a commercial Pt/C catalyst. The H2--O2 alkaline fuel cell test of CoO@Co/N-C as the cathode reveals a maximum power density of 237 mW.cm 2. Detailed investigation clarifies that a synergistic effect, induced by C-N, Co-N-C, and CoO/Co moieties, is responsible for the bulk of the gain in catalytic activity.

NiCoSe2/Ni3Se2 lamella arrays grown on N-doped graphene nanotubes with ultrahigh-rate capability and long-term cycling for asymmetric supercapacitor

In this paper, we report a one-step electrodeposited synthesis strategy for directly growing NiCoSe2/Ni3Se2 lamella arrays(LAs) on N-doped graphene nanotubes(N-GNTs) as advanced free-standing positive electrode for asymmetric supercapacitors. Benefiting from the synergetic contribution between the distinctive electroactive materials and the skeletons, the as-constructed N-GNTs@NiCoSe2/Ni3-Se2LAs present a specific capacitance of ~1308 F g^-1 at a current density of 1 A g^-1. More importantly, the hybrid electrode also reveals excellent rate capability(~1000 F g^-1 even at 100 A g^-1) and appealing cycling performance(~103.2% of capacitance retention over 10,000 cycles). Furthermore, an asymmetric supercapacitor is fabricated by using the obtained N-GNTs@NiCoSe2/Ni3Se2LAs and active carbon(AC) as the positive and negative electrodes respectively,which holds a high energy density of 42.8 W h kg^-1 at 2.6 k W kg^-1, and superior cycling stability of ~94.4% retention over 10,000 cycles. Accordingly, our fabrication technique and new insight herein can both widen design strategy of multicomponent composite electrode materials and promote the practical applications of the latest emerging transition metal selenides in next-generation high-performance supercapacitors.

Filling and unfilling carbon capsules with transition metal oxide nanoparticles for Li-ion hybrid supercapacitors:towards hundred grade energy density

Li-ion hybrid supercapacitors （Li-HECs） facilitate effective combination of the advantages of supercapacitors and Li-ion batteries （LIBs）. However, challenges remain in designing and preparing suitable anode and cathode materials, which often require tedious and expensive procedures. Herein, we demonstrated that hollow N-doped carbon capsules （HNC） with and without a Fe304 nanoparticle core can respectively function as the anode and the cathode in very-high-performance Li-HECs. The Fe3Oa@NC anode exhibited a high reversible specific capacity exceeding 1530 mA h g^-1 at 100 mA g^-1 and excellent rate capability （45% capacity retention from 0.1 to 5 A g^-1） and cycle stability （〉97% retention after 100 cycles）. Moreover, high rate performance was achieved in a full-cell using the HNC cathode. By combining the respective structural advantages of the components, the hybrid device with Fe3Oa@NC//HN C exhibited a remark- able energy density of 185 W h kg^-1 at a power density of 39 W kg^-1. The hybrid device furnished a battery-inaccessible power density of 28 kW kg^-1 with rapid charging/discharging within 9 s at an energy density of 95 W h kg^-1.

Preparation,characterization and densification studies of W-Ag nanocomposites produced by chemical route

W-Ag has applications in a wide range of cutting-edge fields,counting heat sinks and microwave absorbers for micro—electronic components,electric arc ends,and filaments for welding processes,electrical contacts,and durable electronic connections.Chemical methods provide a number of benefits,including improved purity,and controlled particle size.The present study focused on the fabrication of W-Ag nano composites using chemical synthesis.W-Ag nanocomposites with average size less than 50 nm were synthesized using Tungsten hexacarbonyl(W(CO)_(6),and silver acetate(CH_(3)-COOAg)as metal precursors in the present study.The W-Ag composites were sintered using conventional sintering.X-ray diffraction studies of as-prepared powders showed amorphous W-phase and FCC Ag,while sintered W-Ag composites exhibited crystalline BCC W and FCC Ag phase.The effect of sintering temperature on relative density and mechanical properties of W-Ag sintered compacts was investigated.Relative density in excess of 97.6%,98.2%and 98.8%was achieved for W-20.3 wt.%Ag,W-30.1 wt.%Ag and W-39.8 wt.%Ag composites on conventional sintering at 1000℃ for 1 h.Vickers hardness of 364±10 and 320±8 Hv and 279±6 were achieved for W-20.3 wt.%Ag,W-30.1 wt.%Ag and W-39.8 wt.%Ag composite compacts respectively.The hardness value of W-Ag composites decreased with an increase in Ag content.The combination of properties realized in this study renders the composites suitable for automotive and heat sink applications.