Surface Review and Letters

Thermal oxidation (TO) treatments were performed at 873 K, 898 K, 923 K, 948 K, 973 K, 998 K and 1023 K for 10 h in air to improve the wear and corrosion resistance of Ti6Al4V alloy. The effect of TO temperature on microstructural characterizations and surface properties of the obtained TO layers were investigated. The results showed that TO layers with various thickness values were formed on Ti6Al4V alloy under different temperatures. The thickness of the TO layers increased with the increasing of TO temperature. TO layer that was obtained at 973 K suggested the highest surface hardness and the best wear resistance. TO layer that was realized at 948 K exhibited superior corrosion resistance to other TO layers. TO treatment could be considered as an effective method for preventing wear and corrosion of Ti6Al4V alloy.

A novel and simple approach for preparing nanoporous binder free Sn:Pb composite metal foam has been demonstrated. The anodized metallic composite block was functionalized and also found a nanoporous structure. A scanning electron microscopy (SEM) result shows that the nanoflake-like arrangement has synthesized. The X-ray diffraction (XRD) results confirm the nanoporous structure of the Sn/Pb foam after etching with 6 M NaOH. The prepared Sn:Pb metal foam is able to be used as a super capacitors electrode to offer large areal capacitance with regards to the synergic integration of Sn and Pb metals and the unique nanoporous structure.

In this study, Sn-Ag-Ti ternary alloy has been used as the active solder to braze pure aluminum and graphite in atmospheric conditions using ultrasonic vibration as an aid. The authors studied the formation, composition and decomposition temperature of the surface oxides of the active solder under atmospheric conditions. In addition, the wettability of Sn-5Ag-8Ti active solder on the surface of pure aluminum and graphite has also been studied. The results showed that the major components presented in the surface oxides formed on the Sn-5Ag-8Ti active solder under ambient conditions are TiO, TiO₂, Ti₂O₃, Ti₃O₅ and SnO₂. Apart from AgO and Ag₂O₂, which can be decomposed at the brazing temperature (773 K), other oxides will not be decomposed. The oxide layer comprises composite oxides and it forms a compact layer with a certain thickness to enclose the melted solder, which will prevent the liquid solder from wetting the base metals at the brazing temperature. After ultrasonic vibration, the oxide layer was destroyed and the liquid solder was able to wet and spread out around the base materials. Furthermore, better wettability of the active solder was observed on the surface of graphite and pure aluminum at the brazing temperature of 773–823 K using ultrasonic waves. The ultrasonic wave acts as the dominant driving factor which promotes the wetting and spreading of the liquid solder on the surface of graphite and aluminum to achieve a stable and reliable brazed joint.

In this paper, we systematically drew a series of inverse-microemulsion quasi-ternary system phase diagrams of OP-10+C₈H₁₇OH+C₆H₁₂+brine (CaCl₂/BaCl₂) by adjusting the ratio of CaCl₂ and BaCl₂. On this basis, microemulsions have been prepared with seven different molar ratios of Ca²⁺/Ba²⁺, and calcium carbonate and barium carbonate coprecipitation products were obtained by reaction with an equimolar amount of sodium carbonate. The influence of barium ion to morphology and composition of nanometer calcium carbonate were studied. These samples were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The SEM photographs indicated that when the content of Ca²⁺ was higher, some incomplete large cube of coprecipitation particles were formed in solution, but with the content of Ba²⁺ increased gradually, they formed a large number of small spherical particles, with the further increase of Ba²⁺ concentration, the particles mainly had structures of irregular polyhedron eventually. The measurement results of FTIR and XRD indicated that CaCO₃ coprecipitation products gradually changed from calcite to the vaterite, eventually turned into being aragonite with the further increase of Ba²⁺ concentration.

The electronic structures and the stability of the low-index surface (001), (011) and (111) for MgO were investigated by first-principles method based on density functional theory (DFT). We analyzed the stability of the MgO slab in equilibrium with an arbitrary oxygen environment. The density of states (DOS) and the band structures of MgO slabs were calculated and compared with those of the bulk MgO. Our calculation results reveal that the stabilities of the surface vary with the change of O chemical potential. In addition, the (001) and (011) surfaces are semiconductors, which are similar to that of the bulk MgO. However, the MgO(111) surface exhibits metallic property due to the effect of the surface states, which is different from that of the bulk MgO.

An organic thin film transistor (OTFT) based on pentacene was fabricated with SiO₂ as the gate dielectric material. We have investigated the effects of the thickness of pentacene layer and the organic semiconductor (OSC) material on OTFT devices at two different thicknesses. Au metal was deposited for gate, source and drain contacts of the device by using thermal evaporation method. Pentacene thin film layer was also prepared with thermal evaporation. Our study has shown that the change in pentacene thickness makes a noteworthy difference on the field effect mobility (μ_FET), values, threshold voltages (V_T) and on/off current ratios (I_on/I_off). OTFTs exhibited saturation at the order of μ_FET of 3.92 cm²/Vs and 0.86 cm²/Vs at different thicknesses. I_on/I_off and V_T are also thickness dependent. I_on/I_off is 1 × 10³, 2 × 10² and V_T is 15 V, 27 V of 40 nm and 60 nm, respectively. The optimized thickness of the pentacene layer was found as 40 nm. The effect of the OSC layer thickness on the OTFT performance was found to be conspicuous.

The coating oriented growth has attracted great attention because of its effect on coating properties. In this paper, the valence electron structures of TiN and Ni were calculated with the empirical electron theory (EET) in solid and molecules for investigating preferred orientation of nitride coatings containing Ni. The calculation results show that Ni₍₁₁₁₎, CrN₍₁₀₀₎ and TiN₍₁₀₀₎ are the maximum crystal-face electron density, respectively. In CrN (or TiN) coatings, if Ni does not form a single nickel phase, CrN₍₁₀₀₎ (or TiN₍₁₀₀₎) preferred orientation appears easily due to its high crystal-face electron density. When Ni exists as a single phase, CrN₍₁₀₀₎/Ni₍₁₁₁₎ (or TiN₍₁₀₀₎/Ni₍₁₁₁₎) with the minimum crystal-face electron density difference is the most likely to appear in the coatings. Furthermore, high crystal-face electron density difference usually implies fine grain microstructure. The calculation results are consistent with the experimental results.

Reinforced concrete is one of the widely used construction materials for bridges, buildings, platforms and tunnels. Though reinforced concrete is capable of withstanding a large range of severe environments including marine, industrial and alpine conditions, there are still a large number of failures in concrete structures for many reasons. Either carbonation or chloride attack is the main culprit which is due to depassivation of reinforced steel and subsequently leads to rapid steel corrosion. Among many corrosion prevention measures, application of corrosion inhibitors play a vital role in metal protection. Numerous range of corrosion inhibitors were reported for concrete protection that were also used commercially in industries. This review summarizes the application of natural products as corrosion inhibitors for concrete protection and also scrutinizes various factors influencing its applicability.

In this work, the electrokinetic characteristics of calcined kaolinite in aqueous solutions has been studied in the presence of the electrolytes of NaCl, KCl, NH₄Cl, NaNO₃, MgCl₂, CaCl₂ and AlCl₃, through electrophoretic measurement. The experimental results have shown that the zeta potential was closely dependent on the valence and concentration of the electrolytic cations, but not on the type of the cations. The higher the valence and the concentration were, the stronger the impact to the zeta potential was. Al³⁺ could reverse the potential sign from negative to positive. In addition, it was found that the monovalent anions of Cl^- and made a big difference to the zeta potential at the same dosage.

In the paper, molecular dynamics simulation with the modified analytical embedded atom method (MAEAM) is applied to study the size effect on the elastic properties of the B2-NiAl nanofilm. The simulation results indicate that there is a critical thickness, which is about 5.38 nm, to distinguish the size dependence of the elastic properties of the nanofilm. On the one hand, these properties, such as the averaged cohesive energy and the bulk modulus, change evidently as the size is smaller than the critical thickness and the change tendency is tightly controlled by the surface atom composition. On the other hand, as the nanofilm size exceeds the critical one, the calculated values of the elastic properties are almost independent of the film thickness. Relatively, the bulk modulus magnitude of the nanofilm is apparently larger than that of the corresponding bulk material. Finally, the inherent mechanisms of the size impacting on the elastic properties of the B2-NiAl nanofilm have been discussed in more detail. The strengthening effect of the bulk modulus results from the smaller multilayer relaxation of the interlayer distance as compared to those of the bulk materials.

A new electrochemical technique to detect hydrogen peroxide (H₂O₂) was developed. The Pt nanoparticles and Bi^III were subsequently assembled on agmatine sulfate (AS) modified glassy carbon electrode (GCE) and the prepared GCE–AS-Pt–Bi^III was characterized by scanning electron microscopy (SEM) with result showing that the flower-like nanostructure of Pt–Bi^III was yielded. Compared with Pt nanoparticles, the flower-like nanostructure of Pt–Bi^III greatly enhanced the electrocatalysis of GCE–AS-Pt–Bi^III towards H₂O₂, which is ascribed to more Pt–OH obtained on GCE–AS-Pt–Bi^III surface for the presence of Bi^III. Based on its high electrocatalysis, GCE–AS-Pt–Bi^III was used to determine the content of H₂O₂ in the sample of sheet bean curd with standard addition method. Meantime, its electrocatalytic activity also was studied.

The composite coatings were fabricated by laser cladding Al/TiN pre-placed powders on Ti–6Al–4V substrate for enhancing wear resistance and hardness of the substrate. The composite coatings were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The sliding wear tests were performed by MM200 wear test machine. The hardness of the coatings was tested by HV-1000 hardness tester. After laser cladding, it was found that there was a good metallurgical bond between the coating and the substrate. The composite coatings were mainly composed of the matrix of β-Ti (Al) and the reinforcements of titanium nitride (TiN), Ti₃Al, TiAl and Al₃Ti. The hardness and wear resistance of the coatings on four samples were greatly improved, among which sample 4 exhibited the highest hardness and best wear resistance. The hardness of the coating on sample 4 was approximately 2.5 times of the Ti–6Al–4V substrate. And the wear resistance of sample 4 was four times of the substrate.