Oxidation behavior and mechanism of aluminum oxynitride (AlON) at elevated temperatures

The oxidation behavior and mechanism of aluminum oxynitride (AlON) powder exposed to air at elevated temperatures between 800°C and 1300°C was investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM), electron spin resonance (ESR), nuclear magnetic resonance (NMR), and simultaneous thermogravimetry, differential thermal analysis, and mass spectrometry techniques (TG-DTA-MS). The weight of AlON gradually increases to a maximum value at 1150°C and then decreases with further heating. Meanwhile, AlON powder undergoes chemical changes, as evidenced by lattice expansion, and turns eventually into alumina. ESR spectra reveal the occurrence of lone pair electrons in the oxidized products and the intensity of corresponding resonance signal increases before disappearing with the increase in temperature. Combined with the results of NMR and TG-DTA-MS, the measured data suggest that Al-N in [AlO₃N] tetrahedron and [AlO₅N] octahedron are gradually oxidized into Al-O-N group with lone pair electrons, which causes continuous weight gain and lattice expansion. Further oxidation at higher temperatures results in alumina and N₂.     

Electro-reduction of Cu2O to Cu in urea/1-ethyl-3-methylimidazolium chloride

Journal of Applied Electrochemistry - Urea/1-ethyl-3-methylimidazolium chloride (urea-EMIC) was developed to electrodeposit Cu from Cu2O at room temperature. Density, viscosity and conductivity of...     

Differences in electrochemical corrosion behaviours between selective laser melted and wrought Ti6Al4V alloys in acid fluoride-containing artificial saliva

Journal of Applied Electrochemistry - In this work, the electrochemical corrosion behaviours of selective laser melted (SLMed) and wrought Ti6Al4V alloys in acid fluoride-containing artificial...     

Degradability and biocompatibility of bioglass/poly(amino acid) composites with different surface bioactivity as bone repair materials

Bioglass (BG) possesses excellent bioactivity and has been widely used in the manufacture of biomaterials. In this study, a composite with different surface bioactivity was fabricated via in situ melting polymerization by incorporating BG and poly(amino acid) (PAA) at a suitable ratio. The structure of the composite was characterized by Fourier transform infrared spectroscopy and XRD. The compressive strength of the BG/PAA composites was 139 MPa (BG:PAA = 30:70). The BG/PAA composites were degradable, and higher BG in composite showed higher weight loss after 4 weeks of incubation in simulated body fluid. In addition, the BG/PAA composite maintained adequate residual compressive strength during the degradation period. The SEM results showed the differences in surface bioactivities of the composites directly, and 30BG/PAA composite showed thicker apatite layer and higher Ca/p than 15BG/PAA. in vitro MG-63 cell culture experiments showed that the composite was noncytotoxic and thus allows cells to adhere, proliferate, and differentiate. This indicates that the composite has good biocompatibility. The implantations in the bone defects of rabbits for 4 and 12 weeks were studied. The composites had good biocompatibility and were capable of guiding new bone formation without causing any inflammation. The composite may be successfully used in the development of bone implants.     

A novel waterborne polyurethane coating modified by highly dispersed nano-boron carbide particles

In this study, waterborne polyurethane (WPU) coatings were modified by adding various compositions of nano-boron carbide (nano-B₄C) particles. In order to achieve proper dispersion of nano-B₄C in WPU and increasing chemical interactions between them, the nano-B₄C particles were treated with polyethylene glycol (PEG) or polypropylene glycol (PPG). The modified surface and microstructure of nano-B₄C were characterized by Fourier transform infrared, scanning electron microscopy and transmission electron microscopy. The deposition experiment was designed to evaluate the dispersion effect of nano-B₄C in PEG or PPG aqueous solution. The physical performance of nano-B₄C modified WPU coatings was measured following the national standards of paints and vanishes. The results revealed that the PEG6000 not only enhanced the interaction between nano-B₄C and WPU but also exhibited a remarkable ability to improve the physical performance of WPU coating. The coating with 15 wt% of nano-B₄C addition exhibited the best performance in terms of abrasion and hardness, which could be attributed to the best uniform dispersion of nano-B₄C particles in PEG6000 aqueous solution.     

Weathering modification of acrylic emulsion by introducing UV absorbing groups

A new kind of UV-absorbing silicon-fluorinated acrylic emulsion was prepared by emulsion polymerization with 4-allyloxy-2-hydroxybenzophenone, 3-methacryloxypropyltrimethoxysilane (MPS) and hexafluorobutyl methacrylate (HFMA) as functional monomers. The emulsion and its coating were characterized by transmission electron microscope, Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy, ultraviolet absorption spectrum,thermo-gravimetric analysis, water contact angle (CA), and artificial accelerated aging test. The results indicated that the emulsion with core-shell structure was synthesized and showed prominent absorption peaks at 320 and 350 nm. The water CA of the coating was increased from 70.2° to 86.7° because of the incorporated HFMAs and MPSs. Both of the initial and final decomposition temperatures of the coating were increased by more than 20°C compared with those of the unmodified coating. After 10 days of accelerated aging, the color difference (ΔE) and rate of loss of gloss (ΔG) were only 2.78% and 5.22%, while those of the unmodified coating were as high as 22.94% and 78.57%, respectively. Because of the UV absorbers were incorporated by chemical reaction, the new coating had a more durable and effective anti-ultraviolet performance compared with the coatings the UV absorbers were introduced by physical blending.     

Antibacterial self-healing anticorrosion coatings from single capsule system

It is highly desirable to develop self-healing anticorrosion coatings with enhanced antibacterial function to prevent the scratched area to be fouled or corroded in harsh environments. Herein, we report antibacterial self-healing anticorrosion coatings via the simple incorporation of the easily synthesized single polymer microcapsule system. Well-defined polymer microcapsules containing isophorone diisocyanate (IPDI) as a healing agent and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as antibacterial molecules were synthesized by one-pot polymerization. The diameter and core fraction were around 30 μm and 90%, respectively. The active DCOIT content in the core material could be precisely controlled by adjusting the DCOIT/IPDI feeding ratio. The DCOIT/IPDI microcapsules-embedded protective coating exhibits an adaptive self-healing anticorrosion property, as shown by electrochemical test under the condition of the salt-water immersion. Furthermore, the self-healing coating showed efficient antibacterial function against Escherichia coli and Pseudomonas aeruginosa, which is due to the released active biocide molecules on the damaged surfaces. In contrast to other systems, this single capsule system without any catalyst is perspective for extending the service time of the antibacterial self-healing materials in harsh environment.     

Self-Diffusion of Iron in Molten Fe-C Alloys

Self-diffusion coefficients of iron in molten Fe-C alloys have been measured by using the capillary method. In addition, the samples have been autoradiographed and sectioned to insure that no significant convection has occurred during the diffusion. The results can be represented by the equation D = 4.3×10^?3 exp (—12.200/RT) for carbon = 4.6 pct and T = 1513° to 1633°K; and D = 1.0×10^?2 exp (—15,700/RT) for carbon = 2.5 pct and T = 1613° to 1673°K. The D values are higher and the heat of activation for diffusion lower in alloys containing more carbon. Calculation based on the Einstein-Stokes equation indicates that the diffusing species is iron ion.     

Mechanical properties of nano-structured Ti-Si-N films synthesized by cathodic arc evaporation

Ti_1−xSi_xN coatings were synthesized by cathodic arc evaporation with plasma-enhancing filter duct, using Ti₈₀Si₂₀ alloy target as cathodes. Optical emission study revealed that excitation, ionization and charge transfer reactions of the Ti-Si-N plasma occurred during the Ti_1−xSi_xN deposition process. The chemical content of Si varied from 3.3 to 6.0 at% in Ti_1−xSi_xN depending on the nitrogen partial pressure of the reaction chamber. All the Ti_1−xSi_xN coatings displayed a NaCl structure and a preferred (2 0 0) orientation parallel to the substrate surface. Among the studied Ti_1−xSi_xN coatings, the Ti_1−xSi_xN with 6 at.% Si possessed the highest hardness of 45 GPa and H³/E*² ratio of 0.527 GPa, indicating the best resistance to plastic deformation. We found that the structure and mechanical properties of the Ti_1−xSi_xN films were correlated with the nitrogen pressure and silicon content of the coatings.     

真空增压铸造技术及其应用前景

详细论述了真空增压铸造的技术原理、工艺特性及技术优点。结合铝合金铸件大型、复杂、薄壁、整体化和高气密性的发展趋势，针对性地分析了真空增压铸造技术推广应用的适应性，并提出了相应的技术对策。