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.

High temperature lubrication performance of chlorophenyl silicone oil

Most studies of liquid lubricants were carried out at temperatures below 200°C.However,the service temperature of lubricants for aerospace and aeroengine has reached above 300°C.In order to investigate the friction mechanism and provide data for high temperature lubrication,the friction and wear properties of chlorophenyl silicone oil(CPSO)-lubricated M50 steel and Si3N4 friction pairs were investigated herein.Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature.Below 150°C,coefficient of friction(COF)remains at 0.13–0.15 after the short running-in stage(600 s),while the COF in the running-in stage is 0.2–0.3.At 200°C and above,the running-in time is much longer(1,200 s),and the initial instantaneous maximum COF can reach 0.5.Under this condition,the COF gradually decreases and finally stabilizes at around 0.16–0.17 afterwards.This phenomenon is mainly due to the different thickness of boundary adsorption film.More importantly,the wear rate of M50 steel increases significantly with the temperature,while the wear rate barely changes at temperatures above 200°C.The anti-wear mechanism is explained as tribochemical reactions are more likely to occur between CPSO and steel surface with the increased temperature,generating the FeCl2 protective film on the metal surface.Accordingly,FeCl2 tribochemical film improves the lubrication and anti-wear capacity of the system.At high temperatures(200–350°C),FeCl2 film becomes thicker,and the contact region pressure becomes lower due to the larger wear scar size,so the wear rate growth of M50 steel is much smaller compared with that of low temperatures(22–150°C).The main findings in this study demonstrate that CPSO lubricant has good anti-wear and lubrication capacity,which is capable of working under temperatures up to 350°C.

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.