Ultrastable Lubricating Properties of Robust Self-Repairing Tribofilms Enabled by in Situ-Assembled Polydopamine Nanoparticles.

Aqueous lubrication in nature is attracting increasing attention in the tribological fields for reducing friction energy consumption and improving anti-wear durability. Generally, adding nanolubricant additives is one of the most important strategies to effectively enhance the interface performance under boundary lubrication via the formation of a protective tribofilm on rubbing surfaces. However, the adsorbed tribofilms are unstable and are prone to failure during friction, and the interaction mechanism between the tribofilms and frictional interfaces is partly disclosed. In this study, inspired by mussels, an in situ-assembled polydopamine (PDA) tribofilm is achieved with PDA nanoparticles as aqueous lubricant additives, which shows excellent lubrication properties. The coefficient of friction is interface-independent and is reduced by as much as 83%. The results show that the PDA tribofilm can not only form chemical bonding with metal interfaces but also present a synergistic lubrication effect with the upper ceramic surface. Especially, a self-repairing effect of the PAD tribofilm is observed, by which the ultrastable lubricating properties can be achieved during friction, and thus, the friction and wear can be effectively controlled. This work provides an effective method for improving the interface stability of friction pairs under aqueous lubrication and also shows great meaning for industrial applications.

The impact of sphingosine kinase 1 on the prognosis of hepatocellular carcinoma patients with portal vein tumor thrombus.

BACKGROUND: Though there is considerable evidence that sphingosine kinase 1(SPHK1) plays a key role in hepatocellular carcinoma(HCC) progression, the prognostic value of SPHK1 expression in HCC with portal vein tumor thrombus (PVTT) remains unclear. Aims. The purpose of this study was to investigate the relationship of SPHK1 expression with PVTT and HCC recurrence after hepatectomy. METHODS: After screening of gene expression profiling of tumor cell lines, real-time PCR and immunohistochemistry were used to investigate the SPHK1 expression in PVTT and HCC samples. The clinical data of 199 HCC patients with nonmain PVTT who underwent liver resection with curative intention were studied. RESULTS: We identified SPHK1 as the most over-expressed gene in PVTT via gene expression profiling of one human PVTT cell line (CSQT-2). SPHK1 expression was an independent factor affecting survival (hazard ratio [HR] 1.799, 95% confidence interval [CI] 1.337-2.368, P < 0.001) and tumor recurrence (HR 1.451, 95% CI 1.087-1.935, P = 0.011). Patients with SPHK1 over-expression had a poorer prognosis than those with SPHK1 under-expression (P < 0.001 and P = 0.011 for survival and tumor recurrence). CONCLUSIONS: SPHK1 might represent a novel and useful prognostic marker of HCC progression in patients with PVTT.

Tribocorrosion and Surface Protection Technology of Titanium Alloys: A Review.

Titanium alloy has the advantages of high specific strength, good corrosion resistance, and biocompatibility and is widely used in marine equipment, biomedicine, aerospace, and other fields. However, the application of titanium alloy in special working conditions shows some shortcomings, such as low hardness and poor wear resistance, which seriously affect the long life and safe and reliable service of the structural parts. Tribocorrosion has been one of the research hotspots in the field of tribology in recent years, and it is one of the essential factors affecting the application of passivated metal in corrosive environments. In this work, the characteristics of the marine and human environments and their critical tribological problems are analyzed, and the research connotation of tribocorrosion of titanium alloy is expounded. The research status of surface protection technology for titanium alloy in marine and biological environments is reviewed, and the development direction and trends in surface engineering of titanium alloy are prospected.

Engineering Active-Site-Induced Homogeneous Growth of Polydopamine Nanocontainers on Loading-Enhanced Ultrathin Graphene for Smart Self-Healing Anticorrosion Coatings.

Engineering nanocontainers with encapsulated inhibitors onto graphene has been an emerging technology for developing self-healing anticorrosion coatings. However, the loading contents of inhibitors are commonly limited by inhomogeneous nanostructures of graphene platforms. Here, we propose an activation-induced ultrathin graphene platform (UG-BP) with the homogeneous growth of polydopamine (PDA) nanocontainers encapsulated with benzotriazole (BTA). Ultrathin graphene prepared by catalytic exfoliation and etching activation provides an ideal platform with an ultrahigh specific surface area (1646.8 m2/g) and homogeneous active sites for the growth of PDA nanocontainers, which achieves a high loading content of inhibitors (40 wt %). The obtained UG-BP platform exhibits pH-sensitive corrosion inhibition effects due to its charged groups. The epoxy/UG-BP coating possesses integrated properties of enhanced mechanical properties (>94%), efficient pH-sensitive self-healing behaviors (98.5% healing efficiency over 7 days), and excellent anticorrosion performance (4.21 × 109 Ω·cm2 over 60 days), which stands out from previous related works. Moreover, the interfacial anticorrosion mechanism of UG-BP is revealed in detail, which can inhibit the oxidation of Fe2+ and promote the passivation of corrosion products by a dehydration process. This work provides a universal activation-induced strategy for developing loading-enhanced and tailor-made graphene platforms in extended smart systems and demonstrates a promising smart self-healing coating for advanced anticorrosion applications.

Corrosion Behavior of Nitrided Layer of Ti6Al4V Titanium Alloy by Hollow Cathodic Plasma Source Nitriding.

Ti6Al4V titanium alloys, with high specific strength and good biological compatibility with the human body, are ideal materials for medical surgical implants. However, Ti6Al4V titanium alloys are prone to corrosion in the human environment, which affects the service life of implants and harms human health. In this work, hollow cathode plasm source nitriding (HCPSN) was used to generate nitrided layers on the surfaces of Ti6Al4V titanium alloys to improve their corrosion resistance. Ti6Al4V titanium alloys were nitrided in NH3 at 510 °C for 0, 1, 2, and 4 h. The microstructure and phase composition of the Ti-N nitriding layer was characterized by high-resolution transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. This modified layer was identified to be composed of TiN, Ti2N, and α-Ti (N) phase. To study the corrosion properties of different phases, the nitriding 4 h samples were mechanically ground and polished to obtain the various surfaces of Ti2N and α-Ti (N) phases. The potentiodynamic polarization and electrochemical impedance measurements were conducted in Hank's solution to characterize the corrosion resistance of Ti-N nitriding layers in the human environment. The relationship between corrosion resistance and the microstructure of the Ti-N nitriding layer was discussed. The new Ti-N nitriding layer that can improve corrosion resistance provides a broader prospect for applying Ti6Al4V titanium alloy in the medical field.

Effect of Rapid Hollow Cathode Plasma Nitriding Treatment on Corrosion Resistance and Friction Performance of AISI 304 Stainless Steel.

Low-temperature plasma nitriding of austenitic stainless steel can ensure that its corrosion resistance does not deteriorate, improving surface hardness and wear performance. Nevertheless, it requires a longer processing time. The hollow cathode discharge effect helps increase the plasma density quickly while radiatively heating the workpiece. This work is based on the hollow cathode discharge effect to perform a rapid nitriding strengthening treatment on AISI 304 stainless steels. The experiments were conducted at three different temperatures (450, 475, and 500 °C) for 1 h in an ammonia atmosphere. The samples were characterized using various techniques, including SEM, AFM, XPS, XRD, and micro-hardness measurement. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were employed to assess the electrochemical behavior of the different samples in a 3.5% NaCl solution. The finding suggests that rapid hollow cathode plasma nitriding can enhance the hardness, wear resistance, and corrosion properties of AISI 304 stainless steel.

In Situ Green Synthesis of the New Sandwichlike Nanostructure of Mn3O4/Graphene as Lubricant Additives.

Nanoparticles and two-dimensional (2D) nanosheets are well-investigated as lubricant additives, which can significantly reduce frictional energy consumption. However, the tribological properties of the additives will deteriorate because of the occurrence of aggregation in the lubricant and the difficulty in entering the frictional contact area. In the present work, the new sandwichlike nanostructure of Mn3O4 nanoparticles and graphene nanosheets (Mn3O4@G) has been developed by an in situ green synthesis method; i.e., the impurities of Mn2+ ions in crude graphite oxide as the precursor are directly transferred into Mn3O4 precipitate between the graphene sheets. The graphene has a lamellar structure without folds and wrinkles, and the Mn3O4 nanoparticles are not only uniformly anchored on the graphene surfaces but also intercalated in the layers of the graphene nanosheets. The Mn3O4@G exhibits excellent tribological properties and high stability because of a synergistic lubrication effect between the graphene nanosheets and the Mn3O4 nanoparticles. Even at an ultralow concentration (0.075 wt %) and a high temperature of 125 °C, the friction coefficient and the wear depth have been reduced by 75% and 97% compared with base oil, respectively. The synthesis method and the Mn3O4@G nanocomposite have significant potential in various tribological applications for saving energy.

A novel route to the synthesis of an Fe3O4/h-BN 2D nanocomposite as a lubricant additive.

Two-dimensional (2D) nanocomposites as lubricant additives have been widely studied, but the synthetic process of the nanocomposites is not always environmentally friendly or economical. In this study, a new 2D nanocomposite, Fe3O4/h-BN, has been prepared by physical mixing of exfoliated h-BN nanosheets and organically modified Fe3O4 nanoparticles. The nanocomposite displays a unique 2D-layered structure without folds or wrinkles. The Fe3O4 nanoparticles are uniformly dispersed on the h-BN nanosheet surfaces with the help of an elegant self-assembly strategy from van der Waals interactions. For the first time, Fe3O4/h-BN is studied as a lubricant additive and it exhibits excellent tribological properties. The coefficient of friction (COF) and the wear depth can be respectively reduced by 47% and 80% compared with the base oil. Based on the advantages of a simple and low-cost synthetic process and significant tribological properties, Fe3O4/h-BN offers great potential for lubrication application.

Aminosilanization nanoadhesive layer for nanoelectric circuits with porous ultralow dielectric film.

An ultrathin layer is investigated for its potential application of replacing conventional diffusion barriers and promoting interface adhesion for nanoelectric circuits with porous ultralow dielectrics. The porous ultralow dielectric (k ≈ 2.5) substrate is silanized by 3-aminopropyltrimethoxysilane (APTMS) to form the nanoadhesive layer by performing oxygen plasma modification and tailoring the silanization conditions appropriately. The high primary amine content is obtained in favor of strong interaction between amino groups and copper. And the results of leakage current measurements of metal-oxide-semiconductor capacitor structure demonstrate that the aminosilanization nanoadhesive layer can block copper diffusion effectively and guarantee the performance of devices. Furthermore, the results of four-point bending tests indicate that the nanoadhesive layer with monolayer structure can provide the satisfactory interface toughness up to 6.7 ± 0.5 J/m(2) for Cu/ultralow-k interface. Additionally, an annealing-enhanced interface toughness effect occurs because of the formation of Cu-N bonding and siloxane bridges below 500 °C. However, the interface is weakened on account of the oxidization of amines and copper as well as the breaking of Cu-N bonding above 500 °C. It is also found that APTMS nanoadhesive layer with multilayer structure provides relatively low interface toughness compared with monolayer structure, which is mainly correlated to the breaking of interlayer hydrogen bonding.