Kangning Sun

Microstructure, hardness, and bending strength of carbon nanotube-iron aluminide composites

Iron aluminide (Fe3Al) composites reinforced with ~3 wt% of carbon nanotube (CNT) were fabricated by hot press consolidation. Ambient-temperature mechanical properties of the iron aluminide—CNT composites were determined. The hardness, compressive yield strength, and bending strength hardness of composites were higher by 63%, 1%, and 5%, respectively. Microscopic examination of the composite showed the added CNTs still keep their tubular structure. The preliminary results on the processing and improvement in mechanical properties of CNT-reinforced iron aluminide matrix composites are being reported here for the first time.

Fabrication and mechanical properties of β-sialon–Fe x Si y –CNTs composites

Silicon nitride composites were fabricated by adding Fe3Al and carbon nanotubes and hot-pressing at a low sintering temperature of 1600xa0°C. The resulted composites were characterized by X-ray diffraction, Fourier-transform infrared spectrum, and field emission scanning electron microscopy. It was found that the Fe3Al could react with Si3N4 to form the series of compound of FexSiy, and CNTs could keep chemical stability in the system. Mechanical properties of the composites were also investigated. For Fe3Al as the additive, the relative density could reach to 93.6xa0% with the maximum hardness of 15.7xa0GPa. When the Fe3Al and CNTs were added into matrix simultaneously, the relative density reached to 92.6xa0%, and the maximum fracture toughness was 6.7xa0MPaxa0m1/2. Finally, the toughening mechanism of Fe3Al and CNTs in sialon composites, containing crack deflection and bridging, and nanotubes pullout and bridging, were also discussed.

Effect of Adding Carbon Nanotubes on Stress of Fe3Al Intermetallics

Analyses on the stress in the carbon nanotube/Fe3Al composites were performed. The biphase interface valence electron structure was established on the basis of Paulings nature of the chemical bond. The stress occurs by the huge interface electron density difference, which will block the Fe3Al grain agglomeration and growth. With the X-ray diffractions, the calculated magnitude of compressive stress existing in the CNT/Fe3Al interface is 0.38 GPa. The experimental result verifies that the stress has a positive effect on the enhancement of mechanical properties of composite.

VALENCE ELECTRON STRUCTURE ANALYSIS OF INTERFACE OF FeAl/TiN COMPOSITES

Based on Paulings nature of chemical bond, the valence electron structures of TiN and FeAl have been constructed, and the relative electron density differences (REDD) between the low index plane of TiN and FeAl, respectively, have been calculated. [110] FeAl//[110]TiN crystallography orientation has been set up from the minimization of the electron density difference across the interface. From the viewpoint of improving the mechanical properties of composites, the formation of such structures must been engineered in the fabrication processing.

Interface electron structure of Fe3Al/TiC composites

Abstract Based on YUs solids and molecules emperical electron theory(EET), interface valence electron structure of TiC-Fe 3 Al composites was set up, and the valence electron density of different atomic states TiC and Fe 3 Al composites in various planes was determined. The results indicate that the electron density of (100) Fe 3 Al is consistent with that of (110) TiC in the first-class approximation, the absolute value of minimum electron density difference along the interface is 0.007 37 nm −2 , and the relative value is 0.759%. (110) TiC //(100) Fe 3 Al preferred orientation is believed to benefit the formation of the cuboidal shape TiC. In the other hand, it shows that the particle growth is accompanied by the transport of electron, the deviation continuity of electron density intrinsically hinders the grain growth. The electron density of (100) TiC is not consistent with Fe 3 Al arbitrary crystallographic plane, thus it well explains that the increased titanium and carbon contents do not increase the size of large particles. The crystallographic orientation of (110) TiC //(100) Fe 3 Al will improve the mechanical properties. Therefore interface electron theory is an effective theoretical implement for designing excellent property of composites.

Thermoelectric properties of CNTs/Mn0.7Zn0.3Fe2O4 composite fabricated by spark plasma sintering

As a new kind of environment-friendly material, thermoelectric material has got more and more attention and rapid development. In this work, the CNTs/Mn0.7Zn0.3Fe2O4 composite was fabricated by spark plasma sintering (SPS) technique, and the influence of SPS temperature on the thermoelectric properties was discussed. The average grain sizes increased from 50 to 400 nm with increasing SPS temperature from 600 °C to 800 °C. The electrical conductivity of CNTs/Mn0.7Zn0.3Fe2O4 composite demonstrated a typical semiconducting-like behavior, and the value can reach about 77 s m−1, which increased by 4–8 orders of magnitude in comparison with that of traditional Mn–Zn ferrites. The Seebeck coefficient was negative suggesting a n-type conduction, and its value was about −128 ~ −213 μV K−1. By optimizing the sintering temperature, the power factor is significantly improved and the thermal conductivity is reduced simultaneously, which results in a ZT value of about 0.083. These results demonstrate that the CNTs/Mn0.7Zn0.3Fe2O4 composite is a potential thermoelectric material.

Novel composite films of polysaccharides and glutathione capped zinc selenide (GSH@ZnSe) quantum dots for detection of Cd2+ and Cu2+

Water-soluble glutathione capped zinc selenide (GSH@ZnSe) quantum dots (QDs) were employed to develop composite films with two polysaccharides, i.e. positively charged chitosan (CS) and negatively charged xanthan gum (XG), respectively. Both fluorescent and electrochemical strategies were used to detect Cd2+ and Cu2+. The composite films were deposited on a glass substrate and the detection of Cd2+ and Cu2+ was achieved by monitoring fluorescence quenching of the QDs. Compared to XG, which was highly soluble in water, CS acted as an insoluble matrix for QDs and provided good adhesion to the glass substrate. The fluorescence of GSH@ZnSe/CS decreased linearly with the increase in concentration of metal ions, suggesting that the material could be a potential candidate for quantitative detection of Cd2+ and Cu2+. Compared with QD solutions, such a composite film could prominently facilitate the exploitation of QD sensors for device construction. The composites were also deposited onto MWCNT modified glassy carbon (GC) electrodes to detect the electrochemical oxidation of Cd2+ and Cu2+. Electrodes with GSH@ZnSe/XG/MWCNT film had good stability and demonstrated a sensitive detection of Cd2+ and Cu2+ with stripping peak intensity increasing linearly with metal ion concentration. In addition, Cd2+ and Cu2+ could be resolved in a single linear sweep voltammogram (LSV), which was impossible when using the fluorescence quenching technique.

A new persistent luminescent composite for tracing toxic air particulate matter

Air pollution is a major health issue, notably due to the presence of potentially toxic particulate matter with a diameter of lower than or equal to 2.5xa0µm, named ‘PM2.5.’ There is, however, few precise knowledge on the sources, fate and toxicity of particulate matter, notably because there is a lack of method to trace particulate matter in the long term and over large distances. Therefore, we prepared here a novel persistent luminescent tracer composite by incorporating Zn3Ga2GeO8:1%Cr (ZGGO:Cr) persistent luminescence phosphor into PM2.5 precursor followed by freeze drying. Due to a –C=O– chemical bond between PM2.5 and ZGGO:Cr, the obtained composite is well combined and can emit long-lasting persistent emission, of more than 100xa0min, peaking at 696xa0nm, following excitation by a 274xa0nm light. Furthermore, the ZGGO:Cr/PM2.5 composite is performed for simulated ~u20091-cm-thick tissue imaging. The new luminescent PM2.5 composite can be used for environment inspection, imaging, therapy and other complex applications.

Targeting adherence properties of BCG/Fe3O4/chitosan thermosensitive gel integrated materials for irrigation of bladder

Abstract Intravesical instillation using Bacillus Calmette–Guerin (BCG) is recognised as one of the best way to prevent the recurrence of bladder cancer. However, BCG would be excreted with the urine after staying about one hour in the bladder, which have a serious impact on its efficacy. This research intends to design a new sustained release injectable BCG integrated composite materials based on freeze dried BCG. The ultimate aim is to make BCG stay longer than 48 h in the bladder. With the traction of the strong magnetic field strength in vitro, Fe3O4 in particles would attach the drug loaded particles to the bladder wall. Adherent drug is prevented from being excreted with the urine by magnetic constraints and the drug achieves sustained release in the bladder. The results of experiments show that the integrated materials is safe and reliable. Targeting adherence time exceeds 48 h.

Microstructure and Mechanical Properties of Piezoelectric Materials Toughening Multi-walled Carbon Nanotubes/Hydroxyapatite Biocomposites

Multi-walled carbon nanotubes (MWCNTs)/hydroxyapatite (HAp) biocomposites reinforced by lead zirconate titanate (PZT) or lithium niobate (LiNbO3) were prepared at 950xa0°C by hot pressing. The mechanical test results show that the MWCNTs/LiNbO3/HAp (CLH) composite has excellent flexural strength and fracture toughness, about 44 and 110% increase as compared with those of the MWCNTs/HAp (CH) composite. However, dense MWCNTs/PZT/HAp (CPH) composite could not be prepared due to serious evaporation of Pb. Based on in-depth observation of microstructure by field-emission scanning electron microscopy, the toughening mechanism in the CLH composite was discussed.