Fretting-corrosion mechanisms of Ti6Al4V against CoCrMo in simulated body fluid under various fretting states

Ti6Al4V alloy‒CoCrMo alloy pair is commonly applied for modular head‒neck interfaces for artificial hip joint.Unfortunately,the fretting corrosion damage at this interface seriously restricts its lifespan.This work studied the fretting corrosion of Ti6Al4V‒CoCrMo pair in calf serum solution.We established this material pair’s running condition fretting map(RCFM)regarding load and displacement,and revealed the damage mechanism of this material pair in various fretting regimes,namely partial slip regime(PSR),mixed fretting regime(MFR),and gross slip regime(GSR).The damage mechanism of Ti6Al4V alloy was mainly abrasive wear induced by CoCrMo alloy and tribocorrosion.Adhesive wear(material transfer)also existed in MFR.The damage mechanism of CoCrMo alloy was mainly abrasive wear induced by metal oxides and tribocorrosion in GSR and MFR,while no apparent damage in PSR.Furthermore,a dense composite material layer with high hardness was formed in the middle contacting area in GSR,which reduced the corrosion and wear of Ti alloys and exacerbated damage to Co alloys.Finally,the ion concentration maps for Ti and Co ions were constructed,which displayed the transition in the amount of released Ti and Co ions under different displacements and loads.

A healable, mechanically robust and ultrastretchable ionic conductive elastomer for durably wearable sensor

The ionic conductive elastomers show great promise in multifunctional wearable electronics,but they currently suffer from liquid leakage/evaporation or mechanical compliance.Developing ionic conductive elastomers integrating non-volatility,mechanical robustness,superior ionic conductivity,and ultra-stretchability remains urgent and challenging.Here,we developed a healable,robust,and conductive elastomer via impregnating free ionic liquids(ILs)into the ILs-multigrafted poly(urethane-urea)(PUU)elastomer networks.A crucial strategy in the molecular design is that imidazolium cations are largely introduced by double-modification of PUU and centipede-like structures are obtained,which can lock the impregnated ILs through strong ionic interactions.In this system,the PUU matrix contributes outstanding mechanical properties,while the hydrogen bonds and ionic interactions endow the elastomer with self-healing ability,conductivity,as well as non-volatility and transparency.The fabricated ionic conductive elastomers show good conductivity(3.8×10^(-6) S·cm^(-1)),high mechanical properties,including tensile stress(4.64 MPa),elongation(1470%),and excellent healing ability(repairing efficiency of 90%after healing at room temperature for 12 h).Significantly,the conductive elastomers have excellent antifatigue properties,and demonstrate a highly reproducible response after 1000 uninterrupted extension-release cycles.This work provides a promising strategy to prepare ionic conductive elastomers with excellent mechanical properties and stable sensing capacity,and further promote the development of mechanically adaptable intelligent sensors.

Nocturnal atmospheric chemistry of NO_(3) and N_(2)O_(5) over Changzhou in the Yangtze River Delta in China

Comprehensive observations of the nocturnal atmospheric oxidation of NO_(3)and N_(2)O_(5)were conducted at a suburban site in Changzhou in the YRD using cavity ring-down spectroscopy(CRDS)from 27 May to 24 June,2019.High concentrations of NO_(3)precursors were observed,and the nocturnal production rate of NO_(3)was determined to be 1.7±1.2 ppbv/hr.However,the nighttime NO_(3)and N_(2)O_(5)concentrations were relatively low,with maximum values of 17.7 and 304.7 pptv,respectively,illustrating the rapid loss ofNO_(3)andN_(2)O_(5).Itwas found that NO_(3)dominated the nighttime atmospheric oxidation,accounting for 50.7%,whileO3 andOH only contributed 34.1%and 15.2%,respectively.For the reactions of NO_(3)with volatile organic compounds(VOCs),styrenewas found to account for 60.3%,highlighting its dominant role in the NO_(3)reactivity.In general,the contributions of the reactions between NO_(3)and VOCs and the N_(2)O_(5)uptake to NO_(3)losswere found to be about 39.5%and 60.5%,respectively,indicating that N_(2)O_(5)uptake also played an important role in the loss of NO_(3)and N_(2)O_(5),especially under the high humidity conditions in China.The formation of nitrate at night mainly originated from N_(2)O_(5)uptake,and the maximum production rate of NO_(3)^(-)reached 6.5 ppbv/hr.The average NOx consumption rate via NO_(3)and N_(2)O_(5)chemistry was found to be 0.4 ppbv/h,accounting for 47.9%of the total NO_(x)removal.The predominant roles of NO_(3)and N_(2)O_(5)in nitrate formation and NO_(x)removal in the YRD region was highlighted in this study.