Evolution mechanism of cyclized structure of PAN-based pre-oxidized fiber during low temperature carbonization process

The low temperature carbonization process is an important stage to realize the structural transition from the organic cyclized structure of PAN based pre-oxidized fiber to the inorganic pseudo-graphite structure of the ultimate carbon fiber. In the present paper, the evolution mechanism of cyclized structure and aggregation structure of PAN stabilized fiber during low temperature carbonization was studied by means of TGA, 13C-NMR, XRD, XPS and Raman. The results indicated that when the heat-treated temperature was lower than 450 °C, the mainly chemical reactions were the dehydrogenation and pyrolysis reactions in acyclic linear molecular chain or partial cyclized structure. At this stage, the growth of cyclized structure was not obvious. While the original ordered structure was destroyed gradually and the internal stress increased significantly. It induced the cyclized structure to be further oriented. When the temperature was higher than 450 °C, the polycondensation and reconstruction in aromatic heterocyclic structure was more important. The early aromatic heterocycles had many different structural scales, poor homogeneity and many defects in the heterocycles. At this stage, a new pseudo-graphite crystalline structure gradually formed and the d-spacing of graphite layer decreased slightly and crystallites size increased slowly with the increase of heat-treated temperature. When the temperature was higher than 550 °C, the pseudo-graphite base structure gradually formed. The d-spacing were further reduced slightly, and the crystallites size increased slowly. A new ordered basis structure was gradually developed into carbon fiber.

Thermal Stability, Hardness, and Corrosion Behavior of the Nickel–Ruthenium–Phosphorus Sputtering Coatings

Nickel–ruthenium–phosphorus, Ni–Ru–P, alloy coatings were fabricated by magnetron dual-gun co-sputtering from Ni–P alloy and Ru source targets. The composition variation and related microstructure evolution of the coatings were manipulated by the input power modulation. The as-prepared Ni–Ru–P alloy coatings with a Ru content less than 12.2 at.% are amorphous/nanocrystalline, while that with a high Ru content of 52.7 at.% shows a feature of crystallized Ni, Ru, and Ru2P mixed phases in the as-deposited state. The crystallized phases for high Ru content Ni–Ru–P coatings are stable against annealing process up to 600 °C. By contrast, the amorphous/nanocrystalline Ni–Ru–P thin films withstand a heat-treated temperature up to 475 °C and then transform into Ni(Ru) and NixPy crystallized phases at an annealing temperature over 500 °C. The surface hardness of the Ni–Ru–P films ranges from 7.2 to 12.1 GPa and increases with the Ru content and the annealing temperatures. A highest surface hardness is found for the 550 °C annealed Ni–Ru–P with a high Ru content of 52.7 at.%. The Ecorr values of the heat-treated amorphous/nanocrystalline Ni–Ru–P coatings become more negative, while with a high Ru content over 27.3 at.% the Ni–Ru–P films show more negative Ecorr values after annealing process. The pitting corrosion feature is observed for the amorphous/nanocrystalline Ni–Ru–P coatings when tested in a 3.5M NaCl solution. Severer pitting corrosion is found for the 550 °C annealed Ni–Ru–P coatings. The development of Ni(Ru) and NixPy crystallized phases during annealing is responsible for the degeneration of corrosion resistance.

Microstructure of Silicon Nitride Fibers at Elevated Temperatures

The composition and microstructure of silicon nitride fibers after heat-treatment at elevated temperatures were investigated by XRD, NMR, XPS, SEM and TEM analyses. The results show that as-received fibers consisted of amorphous silicon nitride, and a little Si-C-O structure. During heat-treatment process, α-Si3N4 and β-Si3N4 formed resulting from the crystallization of amorphous silicon nitride, and the formation of β-SiC derived from the decomposition of Si-C-O structure. As heat-treated temperature increased from 1400oC to 1600oC, the above phenomenon become obvious, indicating that the fiber would possess high serving life with serving temperature lower than 1400oC. The tensile strength of fibers stays stable when heat-treated temperature was below 1200oC, while the strength retention of fibers sharply decreased to 50% after heat-treatment at 1400°C.

Nanoindentation Behaviors of HVOF WC-10Co-4Cr Coating after Heat Treatment

WC-10Co-4Cr cermet coatings were deposited on low carbon steel using the HVOF technique, then heat treated by different process (300 °C × 3 hours, 400 °C × 3 hours, and 500 °C × 3 hours). The influences of heat treatment on microhardness, elasticity modulus of coatings were studied by nanoindentation method in this paper. The results show that the microhardness increased with the heat-treated temperature increasing, but the tendency of elasticity modulus was opposite. In the case of 500 °C × 3 hours heat-treated coating, the microhardness increased by approximately 30% and elasticity modulus decreased by approximately 15% in comparison with that of as-sprayed coating.

Influence of Heat Treated Temperature on the Photoactivating Property of Nanometer ZnO/SnO2 Powder

Nanometer ZnO/SnO2powder was prepared by coprecipitating method with SnCl4•5H2O, ZnNO3•6H2O, HCl, NaOH as raw materials. Influence of heat treated temperature on the photoactivating property and structure and material phase of nanometer ZnO/SnO2(ZnO/SnO2=4/1(mol ratio)) compound photocatalyst powder was studied by X-ray diffraction (XRD) and transmission electron microscope(TEM) and the degradation of methyl orange solution as a reaction model. The results show that the photoactivating activity of ZnO/SnO2powder starts increasing and then decreasing when heat treated temperature increases. The photoactivating activity of ZnO/SnO2powder is maximum, particle size is 20-30 nanometer and dispersion is good when heat treated temperature is 650°C. The photocatalytic activity of ZnO/SnO2powder gradually reduces, dispersion is not good and there is Zn2SnO4crystal phase when heat treated temperature is above 750°C.

Microstructure and Mechanical Properties of Ti1-xAlxN Thin Films

A series of Ti1-xAlxN thin films were deposited by reactive magnetron sputtering. The content, microstructure and the hardness of the thin films were characterized respectively with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and nanoindentor. The effect of Al content on the microstructure and hardness was studied. It was found that Ti1-xAlxN compound thin films exhibits a cubic structure with (1 1 1) preferred orientations and that the lattice parameter of Ti1-xAlxN thin films decrease with the increase of Al content. The hardness of Ti1-x AlxN compound thin films is higher than that of TiN and increases with the increase of Al content. At the heat-treated temperature T = 600 °C, the Ti1-xAlxN thin films is still of high microhardness.

Corrosion Behavior of Electroless Deposited Fe-Zn Coating

In this work, Fe-Zn coating on copper is obtained by electroless plating. The surface mor -phologies and composition of the coatings has been investigated using scanning electronic microscope (SEM) and energy dispersive spectroscopy(EDS). Corrosion behavior of Fe-Zn coating in3.5% NaCl solution is gaved a further insight. The impedance diagram indicates that corrosion resistance of coating is better. The open circuit potential of Fe-Zn coating is at about -1V. Self-corrosion potential of Fe-Zn coating in 3.5%NaCl solution shifts in the positive direction first and then shifts from -0.622V to -0.603V with increasing heat-treated temperature, while corresponding self-corrosion current decreases at first and then. increases Corrosion resistance of coating is the best when heat-treated temperature is 300°C.

Sonocatalytic degradation of organic dyes and influence of Al2O3, Y2O3 and Fe2O3 on catalytic activity of TiO2 under ultrasonic irradiation

In order to improve the sonocatalytic activity of TiO2, Al2O3/TiO2, Y2O3/TiO2 and Fe2O3/TiO2 composites were prepared using mechanical mixing, liquid boiling, ultrasonic dispersion and heat-treated methods. And then, a series of degradation experiments were carried out under ultrasonic irradiation. Also, the influences of heat-treated temperature and heat-treated time on the sonocatalytic activity of Al2O3/TiO2, Y2O3/TiO2 and Fe2O3/TiO2, and ultrasonic irradiation time and solution acidity on the sonocatalytic degradation of Acid red B were investigated by UV-vis spectra. It was found that the degradation ratio showed significant increase in the order TiO2 < Fe2O3/TiO2 < Y2O3/TiO2 < Al2O3/TiO2. And the corresponding percentage degradations are about 37, 45, 52 and 81%, respectively. In addition, for exploring the universality, the degradation of other several organic dyes was also reviewed under the same conditions. Because of good degradation efficiency, this method may be an advisable choice for the treatment of non- or low-transparent wastewaters in the future.

Alkali-Activation Reactivity and Al Environment of Chemosynthetic Al2O3–2SiO2 Powders

In this study, pure Al2O3-2SiO2 powders for a geopolymer were prepared by a sol-gel method, alkali-activation tests and alkali-dissolvability of the powders were carried out, and structure of the powders and alkali-activated products was investigated by 29Si and 27Al MAS NMR and SEM. Results showed that higher alkali-activation reactivity (higher compressive strengths of alkali-activated products) appeared in the powders heat-treated between 600-800 °C and alkali-dissolvability trend was different from that of alkali-activation tests. There were clear correlations between microstructure of alkali-activated products and alkali-activation reactivity and Al environment of the powders. It was found that high strength was related to a dense, fine grained microstructure. Such a structure was found in the alkali-activated products synthesized with the powders with high 5-coordinated Al contents. In addition, the peaks attributed to 5-coordinated Al were strengthened with the rise of heat-treated temperature of the powders.