Advanced Materials Research Vol. 509

Abstract: Ba0.5Sr0.5TiO3:Pr powders co-doped with and without Al were synthesized by citrate-nitride combustion process. To investigate the effect and mechanism of Al dopant, samples with various Al3+ and Pr3+ content were prepared. The excitation and emission spectra were detected. Enhanced red emission around 613 nm was obtained by Al addition. Moreover, an emission at 491 nm was observed. Substitute situation of Pr3+ ions in the lattice was discussed. And the mechanism of energy transition was explained by the model of an intermediate charge transfer state.

Abstract: Cu-based materials reinforced by titanium carbide used in the field of brake or conducting friction were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). X-ray diffraction results indicate that the composites consist of copper matrix, Cu3Ti2, titanium carbide and graphite. Transmission electron microscope (TEM) image shows that a smooth interface exists between the titanium carbide particles and copper matrix. Moreover, the laminate structure of graphite (800°C) transfers to not consistent with the laminate structure at high temperature (1000°C).

Abstract: Large quantities of BN-coated aluminum borate (Al18B4O33) nanowhiskers with typical 20 - 50 nm in diameter and 0.5 - 2 m in length have been successfully synthesized by sol-gel and post-thermal-treatment methods. The dependence of morphology and structures on the synthetic process of the coated nanowhiskers has been investigated systematically. Al4B2O9 nanowhiskers were first prepared at a relative low temperature, and then converted into Al18B4O33 nanowhiskers at higher temperatures in the air due to their high-temperature instability. Besides Al18B4O33phase, Al5BO9 and B2O3 could also be generated in the process of transition. However, if a flow of NH3 gas was introduced during the post-thermal-treatment of Al4B2O9 nanowhiskers, the Al5BO9 and B2O3 phases disappeared and BN-coated Al18B4O33 nanowhiskers were finally obtained. Uniform BN layers were coated on the surface of the nanowhiskers by the interfacial reaction between NH3 and B2O3 vapor which was in-situ generated from the nanowhiskers. The NH3-introducing temperature has a significant effect on the morphology and composition of the nanowhiskers. The BN-coated Al18B4O33nanowhiskers are envisaged to become prime candidates as reinforcement in light metal matrix composites.

Abstract: In this study, the multi-functional gradient pp-F:TMDSO coating had been successfully developed via power-modulated plasma polymerization. The plasma power and gas flow rate of tetramethyldisiloxane and tetrafluoromethane were well controlled to implement a gradient coating to achieve the mechanical property, transmittance, hydrophobic and oleophobic properties. The coating shows that the pencil hardness of 3H and Scotch tape adhesion of 5B demonstrating the protective function of the coating. The water and oil contact angle are 105° and 31.7° respectively. The coated specimen remains an optical transparency of 90% close to bare PC material. Comparing with the commercialized screen protectors, this coating shows superior protective and anti-fingerprint performance.

Abstract: Polymeric materials have been widely used as flexible substrates and housing parts of modern electronic wares. However, their low hardness and scratch resistance must be improved by additional protective surface coatings, which require not only mechanical durability but also additional functions such as surface hydrophobicity, oleophobicity as well as anti-fingerprint performance. To satisfy these, a power modulated plasma polymerization technique was designed to synthesize a transparent compositional gradient coating on polycarbonate (PC) substrate. Firstly, a constant flow rate of tetramethyldisiloxane (TMDSO) precursor was introduced where higher plasma power was employed to deposit a hard H-C-Si-O bottom layer. The plasma power was then decreased meanwhile admitting increased fluoromethane (CF₄) gas flow as the second precursor to obtain a top layer with low surface energy. The hard bottom layer acts as a strong mechanical support and the top layer gives additional hydrophobicity and oleophobicity. Ultimately, the coating shows that a pencil hardness of 3H and Scotch-tape adhesion of 5B improves its protective function. A water contact angle of 105° and oil contact angle of 31.7° can be obtained. The coated specimen remains an optical transparency of 90% close to bare PC material. Comparing with commercialized screen protectors, the developed coating shows superior protective and anti-fingerprint performance.

Abstract: It is importance to be able to predict the hot tearing tendency for multicomponent magnesium alloys. Hot tearing is one of the most common and serious defects that occurs during the solidification of commercial magnesium alloys. Clyne and Davies correlated the susceptibility-composition relationship in binary systems based on the concept of the existence of critical time periods during the solidification process when the structure is most vulnerable to cracking. The present work first evaluates the hot tearing susceptibility (HTS) of binary Mg-Zn system using thermodynamic simulations based on Clyne-Davies’ model, a typical “λ shape” curve is obtained. And then a scaling factor is investigated to obtain the internal-consistent cracking susceptibility coefficient for further investigating the addition of aluminum on the HTS in the ternary Mg-Zn-Al system. The predicted hot tearing tendencies is consistent very well with the experimental results of the Mg-Zn binary system and Mg-Zn-Al ternary system.

Abstract: In the present study, bismuth oxide (Bi₂O₃) powders were prepared from bismuth nitrate at various temperatures by spray pyrolysis (SP). The Bi₂O₃ powder can convert from a monoclinic α phase to a tetragonal β phase at a pyrolysis temperature of > 600° C. The crystallinity of the SP powder increased with the increase of pyrolysis temperature. The resulting SP powders were then mixed with organics and screen-printed onto the surface of LED for the evaluation of ultraviolet (UV) inhibition. The β-type bismuth oxide powder pyrolyzed at 700°C exhibited a fine crystal structure. This caused the efficiency of UV inhibition to be 97.71% when the powder concentration was as low as 9.04 wt%.

Abstract: This study explores a series of optical, thermal, and structural properties based on zinc-aluminum phosphate glasses that doped with varied rare earth (RE) elements Yb2O3 and P2O5 components replaced by SiO2. It was found that for 60P glasses system, 7 mol% Yb2O3 doped has the maximum fluorescence but quenching when Yb2O3 is doped up to 9 mol%. In addition, with increasing the content of Yb2O3 the absorption intensity increased. According to Raman spectra, we found the Yb3+ and Si4+ ions for the impact of network structure of glass, SiO2 added to make the network structure of phosphate glasses at 450-500cm-1 and 600-650cm-1 were formed O-T-O bond and T-O-T bond(T=Si, Al).

Abstract: A new method for removal of impurities in pure molten aluminum has been presented in this paper. The basic principle of this method is that the molten fluxes are forced to inject into the molten aluminum under counter-gravity, creating strong vortex to mix fully with the molten aluminum. In this way, the impurities in the aluminum will transfer into the flux because of the absorption of the flux to the inclusions. As the result, the molten aluminum is purified. The experiments were carried out for pure aluminum combined with the flux (40wt.% NaCl，30wt.% KCl，10wt.% NaF and 20wt.%Na3AlF6). The results show that after 3 purifying cycles (6 minutes), the inclusion contents decreased from 2. 1% to 0.35%, a removal rate of 83.3%; and hydrogen concentration decreased from 0.37ml/100gAl to 0.12ml/100gA, with hydrogen removal rate being 68%.

Abstract: In this paper, corrosion behaviors of 13MnNiMoR steel and its weld joint in the EO reactor service environment were studied. Metallographic analysis and electrochemistry corrosion tests in boiler water which are concerned on different zone metal of 13MnNiMoR steel weld joint have been carried out, and the effect of postweld heat treatment and the pH value of the working medium were discussed. The results indicated that the resistance of different zone metal in joint is tightly connected with their microstructure and heat-affected zone always shows the max corrosion current density. The results also showed that heat treatment could significantly improve the anticorrosion properties of 13MnNiMoR steel weld joint.