Improvement of hydrogen permeation barrier performance by iron sulphide surface films

Fe–S compounds with hexagonal crystal structure are potential hydrogen permeation barrier during H2S corrosion. Hexagonal system Fe–S films were prepared on carbon steel through corrosion and CVD deposition, and the barrier effect of different Fe–S films on hydrogen permeation was tested using electrochemical hydrogen permeation method. After that, the electrical properties of Fe–S compound during phase transformation were measured using thermoelectric measurement system. Results show that the mackinawite has no obvious barrier effect on hydrogen penetration, as a p-type semiconductor, and pyrrhotite (including troilite) has obvious barrier effect on hydrogen penetration,as an n-type semiconductor. Hydrogen permeation tests showed peak permeation performance when the surface was deposited with a continuous film of pyrrhotite (Fe_(1–x)S) and troilite. The FeS compounds suppressed hydrogen permeation by the promotion of the hydrogen evolution reaction, semiconducting inversion from p-to n-type, and the migration of ions at the interface.

Effects of surface morphology on tribological properties of Arapaima gigas scales

The remarkable mechanical adaptability of arapaima(Arapaima gigas)scales has made them an important subject of study.However,no research has been conducted into their tribological properties,which are crucial for the protectability and flexibility of arapaimas.In this study,by combining morphological characterizations,friction experiments,and theoretical analyses,the relationship between the surface morphology and tribological properties of arapaima scales is determined.These results indicate that arapaima scales exhibit varying surface morphologies in different regions.More specifically,the exposed regions of scales feature grooves and a circulus,whereas the covered regions exhibit bumps.The specific surface morphology of arapaima scales produces varying tribological properties across different regions and sliding directions.The unique tribological properties of arapaima scales influence the forces received from predator attacks and neighboring scales,directly influencing the arapaima’s protective capabilities.This study provides new insights into the mechanisms of natural flexible dermal armors,and it has potential applications in personal protective systems.

MoS_(2) reinforced PEEK composite for improved aqueous boundary lubrication

Polyether-etherketone(PEEK)is a corrosion-resistant material that has been widely used in aqueous lubrication.However,its anti-wear performance must be improved for its application in the industry.In this study,to improve the anti-wear performance of PEEK for aqueous boundary lubrication,PEEK/MoS_(2)composites were prepared by ball-milling and spark plasma sintering processes.A competitive MoS_(2)mechanism between the low shear strength property and the role of promoting wear debris generation influences the anti-wear performance of PEEK/MoS_(2)composites.Experiments demonstrated that the coefficients of friction(COF)and wear rate of PEEK composite with 0.25 wt%MoS_(2)were significantly reduced 68%and 94%,respectively.Furthermore,this was the first time that a PEEK composite could achieve a COF of less than 0.05 in aqueous boundary lubrication.Its anti-wear performance was verified to be better than that of PEEK/carbon fiber(CF)and Thordon composites.The PEEK/MoS_(2)composite may be a potential material for underwater equipment because of its outstanding anti-wear performance in aqueous boundary lubrication.

Robust scalable reversible strong adhesion by gecko-inspired composite design

Bio-inspired reversible adhesion has significant potential in many fields requiring flexible grasping and manipulation,such as precision manufacturing,flexible electronics,and intelligent robotics.Despite extensive efforts for adhesive synthesis with a high adhesion strength at the interface,an effective strategy to actively tune the adhesion capacity between a strong attachment and an easy detachment spanning a wide range of scales has been lagged.Herein,we report a novel soft-hard-soft sandwiched composite design to achieve a stable,repeatable,and reversible strong adhesion with an easily scalable performance for a large area ranging from~1.5 to 150 cm2 and a high load ranging from~20 to 700 N.Theoretical studies indicate that this design can enhance the uniform loading for attachment by restraining the lateral shrinkage in the natural state,while facilitate a flexible peeling for detachment by causing stress concentration in the bending state,yielding an adhesion switching ratio of~54 and a switching time of less than~0.2 s.This design is further integrated into versatile grippers,climbing robots,and human climbing grippers,demonstrating its robust scalability for a reversible strong adhesion.This biomimetic design bridges microscopic interfacial interactions with macroscopic controllable applications,providing a universal and feasible paradigm for adhesion design and control.

Synergistic lubricating effect of graphene/ionic liquid composite material used as an additive

We prepared a graphene/ionic liquid(G/IL)composite material by the hybridization of G and an IL for use as a lubricating oil additive.The friction coefficient and wear volume of a base oil containing 0.04 wt%of the G/IL composite was reduced by 45%and 90%,respectively.Furthermore,the base oil containing the G/IL composite exhibited better lubricating properties than the base oil containing G,IL,or a mixture of IL and G at the same mass fraction.A synergistic lubrication mechanism was also revealed.The G/IL composite was adsorbed and deposited on the wear surface,forming a more ordered protective film and a unique tribochemical reaction film during rubbing.Therefore,the G/IL composite exhibited the synergistic lubricating effects of G and IL,which significantly improved the lubricating performance of the base oil.This study also suggested a way to limit the out-of-plane puckering of G at the macroscale.

Quantification/mechanism of interfacial interaction modulated by electric potential in aqueous salt solution

With the development of surface and interface science and technology,methods for the online modulation of interfacial performance by external stimuli are in high demand.Switching between ultra-low and high friction states is a particular goal owing to its applicability to the development of precision machines and nano/micro-electromechanical systems.In this study,reversible switching between superlubricity and high friction is realized by controlling the electric potential of a gold surface in aqueous salt solution sliding against a SiO_(2) microsphere.Applying positive potential results creates an ice-like water layer with high hydrogen bonding and adhesion at the interface,leading to nonlinear high friction.However,applying negative potential results in free water on the gold surface and negligible adhesion at the interface,causing linear ultra-low friction(friction coefficient of about 0.004,superlubricity state).A quantitative description of how the external load and interfacial adhesion affected friction force was developed,which agrees well with the experimental results.Thus,this work quantitatively reveals the mechanism of potential-controlled switching between superlubricity and high-friction states.Controlling the interfacial behavior via the electric potential could inspire novel design strategies for nano/micro-electromechanical and nano/micro-fluidic systems.