Novel Method for Evaluating the Aging of Aviation Turbine Engine Oils via High-Temperature Bearing Deposit Tests

Aviation turbine engine oils require excellent thermal-oxidative stability because of their high-temperature environments.High-temperature bearing deposit testing is a mandatory method for measuring the thermal-oxidative performance of aviation lubricant oils,and the relevant apparatus was improved in the present study.Two different commercial aviation turbine engine oils were tested,one with standard performance(known as the SL oil)and the other with high thermal stability,and their thermal-oxidative stability characteristics were evaluated.After 100 h of high-temperature bearing testing,the SL oil was analyzed by using various analytical techniques to investigate its thermal-oxidative process in the bearing test,with its thermal-oxidative degradation mechanism also being discussed.The results indicate that the developed high-temperature bearing apparatus easily meets the test requirements of method 3410.1 in standard FED-STD-791D.The viscosity and total acid number(TAN)of the SL oil increased with the bearing test time,and various deposits were produced in the bearing test,with the micro-particles of the carbon deposits being sphere-like,rod-like,and sheet-like in appearance.The antioxidant additives in the oil were consumed very rapidly in the first 30 h of the bearing test,with N-phenyl-1-naphthylamine being consumed faster than dioctyldiphenylamine.Overall,the oil thermal-oxidative process involves very complex physical and chemical mechanisms.

Research on the impact of high-temperature aging on the thermal safety of lithium-ion batteries

Understanding the thermal safety evolution of lithium-ion batteries during high-temperature usage conditions bears significant implications for enhancing the safety management of aging batteries.This work investigates the thermal safety evolution mechanism of lithium-ion batteries during high-temperature aging.Similarities arise in the thermal safety evolution and degradation mechanisms for lithium-ion batteries undergoing cyclic aging and calendar aging.Employing multi-angle characterization analysis,the intricate mechanism governing the thermal safety evolution of lithium-ion batteries during high-temperature aging is clarified.Specifically,lithium plating serves as the pivotal factor contributing to the reduction in the self-heating initial temperature.Additionally,the crystal structure of the cathode induced by the dissolution of transition metals and the reductive gas generated during aging attacking the crystal structure of the cathode lead to a decrease in thermal runaway triggering temperature.Furthermore,the loss of active materials and active lithium during aging contributes to a decline in both the maximum temperature and the maximum temperature rise rate,ultimately indicating a decrease in the thermal hazards of aging batteries.

A thermal stress loading technique for large-sized hot dry rock mechanical tests

Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host frames and hydraulic pumps,which could lead to great investment.Low-cost testing machines clearly always have great appeal.In this study,a new approach is proposed using thermal expansion stress to load rock specimens,which may be particularly suitable for tests of deep hot dry rock with high temperatures.This is a different technical route from traditional mechanical loading through hydraulic pressure.For the rock mechanics test system of hot dry rock that already has an investment in heating systems,this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes.This paper presents the basic principle and a typical design of this technical solution.Preliminary feasibility analysis is then conducted based on numerical simulations.Although some technical details still need to be resolved,the feasibility of this loading approach has been preliminarily confirmed.

Development and Validation of a Laboratory Aging Method for the Accelerated Simulation of Reclaimed Asphalt

The paper presented first results elaborated during the European Research Project Re-road which aims at the development of techniques for increasing the recycling rates of reclaimed asphalt. During service life surface asphalt courses are subjected to aging due to oxidation effects which causes the hardening of the binder and thereby a change in the chemical, physical and mechanical properties of the material. Surface courses often contain highly modified binders as well as special additives for improving the performance characteristics. As these layers inhibit the shortest service lives compared to other road construction layers every year high amounts of reclaimed surface asphalt are available for recycling. The question is raised how the reclaimed asphalt consisting of high quality and costly material components can be recycled for optimal added value. To analyze the asphalt mix service life performance and its recyclability during mix design a laboratory method was developed to simulate the real in-situ aging. First the effects of site aging on the binder and asphalt characteristics were presented. Three laboratory aging methods were discussed which aimed the accelerated aging which meets similar property changes as site aging. At last the effects of two different laboratory aging methods on the same SMA mixture were compared.

Thermal fatigue behaviors of SiC power module by Ag sinter joining under harsh thermal shock test

The excellent properties of SiC bring new challenges for the device packaging.In this study,the bonding strength,fracture behaviors and microstructural evolution of micron-porous Ag joint were elevated during thermal cycling(–50 ℃–250 ℃) in SiC/DBC(direct bonding copper) die attachment structure for different time.During harsh thermal shock test,the strength of sintered joint deceased gradually with the increase of cycling number,and the value just was half of the value of as-sintered after 1 000 cycles.Coarsening of Ag grains was observed in micron-porous joint with the structure inhomogeneity and defects increasing,which were the reasons of the strength decease.In addition,it was also found that the fracture behavior of sintered joints was changed from ductile deformation of Ag grain to brittle fracture of crack propagation after 1 000 cycles.This study will add the understanding in the mechanical properties of Ag sinter joining and its applications at high temperature.

Corrosion evolution of high-temperature formed oxide film on pure Sn solder substrate

The evolution of morphology, composition, thickness and corrosion resistance of the oxide film on pure Sn solder substrate submitted to high-temperature aging in 150 °C dry atmosphere was investigated. The results indicate that high-temperature aging accelerates the dehydration of Sn(OH)_(4)in the pre-existing native oxide film to form SnO_(2)and facilitates the oxidation of fresh Sn substrate, resulting in the gradual increase in oxide film thickness and surface roughness with prolonging aging time. However, the corrosion resistance of the film initially is enhanced and then deteriorated with an extending aging time. Besides, the formation and evolution mechanisms of the oxide film with aging time were discussed.

High-Temperature Corrosion of Protective Coatings for Boiler Tubes in Thermal Power Plants

High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.

Optimization of technical measures for improving high-temperature performance of asphalt-rubber mixture

Asphalt-rubber pavements often become dam-aged in high-temperature regions and appear rutted or wavy, and experience slippage. To improve the high-temperature performance of the asphalt-rubber mixture, technical measurements, such as, the optimal adjustment of gradation, technique of composite modification, and control of compaction were investigated. An optimal adjustment of aggregate gradation based on stone matrix asphalt improves the high-temperature stability of the asphaltrubber mixture significantly. Through composite modifi- cation, the effect of asphalt-rubber modification was enhanced, and the dynamic stability and relative defor- mation indices of the asphalt-rubber mixture were improved significantly. Furthermore, compaction parame- ters had a significant influence on the high-temperature stability of the asphalt-rubber mixture. The rolling times for compacting the asphalt-rubber mixture should be controlled to within 18-20 round-trips at a molding temperature at 180℃; if the rolling time is a 12 round-trip, the compaction temperature of the asphalt-rubber mixture should be controlled between 180 and 190℃.

Experimental Evaluation of the Mechanical Properties of Cement Sheath under High-Temperature Conditions

The sealing integrity of cement sheath in offshore wells is seriously threatened under high-temperature conditions,resulting in gas channeling and other problems.Given the lack of experimental results,in this study relevant samples of a cement slurry sealing section of a typical offshore high-temperature well have been prepared and analyzed.In particular,the mechanical properties have been assessed with a triaxial pressure servo instrument and a high-temperature curing kettle.The density and the Poisson’s ratio of the samples have also been tested.The stress-strain curve has been drawn to obtain the elastic modulus and the compressive strength.The rock brittleness index has been calculated according to the measured elastic modulus and the Poisson’s ratio,together with the brittleness and the compressibility of the cement samples.The test results show that the mechanical properties and bonding strength of the cement samples are optimal at 130°C,medium at 150°C,and poor at 180°C.

Effect of cryogenic and aging treatments on low-energy impact behaviour of Ti-6Al-4V alloy

The objective of this study is to examine the effects of cryogenic and aging treatments on the impact strength andmechanical properties of Ti?6Al?4V alloy.To accomplish that objective,cryogenic treatment(CT),aging treatment(AT)andcryogenic treatment followed by aging treatment(CAT)were conducted on Ti?6Al?4V alloy.Impact tests were performed onheat-treated and untreated samples using different impactor nose geometries(hemispherical,60°and90°conical)to determine theeffect of impactor nose geometry on the damage characteristic.The findings showed that energy absorption increased and areas ofdamage decreased as a result of heat treatment in all treated samples.The highest energy absorption was observed in the CATsamples,due to the increase in energy absorption,the smallest damaged area occurred in the CAT sample,and the largestdeformation was seen in the untreated samples.Additionally,it was seen that the damaged area and deflection were stronglydependent on impactor nose geometry.The maximum deflection and narrowest deformation area were seen with60o conical nosegeometry.The deformation area increased with increasing impactor nose angle.

Graphene/carbon structured catalyst layer to enhance the performance and durability of the high-temperature proton exchange membrane fuel cells

In this study,nitrogen doped electrochemically exfoliated reduced graphene oxide and carbon black supported platinum(Pt/Nr EGO_(2)-CB_(3))has been prepared to enhance the performance and durability of hightemperature PEMFCs with lower Pt loading.On the one hand,Pt/Nr EGO_(2)-CB_(3)with the strong interaction between the Pt and nitrogen(N)prevent agglomeration of Pt particles and Pt particles is 5.46±1.46 nm,which is smaller than that of 6.78±1.34 nm in Pt/C.Meanwhile,ECSA of Pt/Nr EGO_(2)-CB_(3)decrease 13.65%after AST,which is much lower than that of 97.99%in Pt/C.On the other hand,the Nr EGO flakes in MEAac act as a barrier to mitigate phosphoric acid redistribution,which improves the formation of triple-phase boundaries(TPBs)and gives stable operation of the MEAacwith a lower decay rate of 0.02 mV h^(-1)within100 h.After steady-state operation,the maximum power density of Pt/Nr EGO_(2)-CB_(3)(0.411 W cm^(-2))is three times higher than that of conventional Pt/C(0.134 W cm^(-2))in high-temperature PEMFCs.After AST,the mass transfer resistance of Pt/Nr EGO_(2)-CB_(3)electrode(0.560Ωcm^(2))is lower than that in Pt/C(0.728Ωcm^(2)).

Property changes of anchor grout calcined ginger nuts admixed with fly ash and quartz sand after accelerated ageing tests

Calcined ginger nuts admixed by fly ash and quartz sand (CGN-(F+S)) has been validated to be basically compatible to earthen sites as an anchor grout. Accelerated ageing tests including water stability test, temperature and humidity cycling test, soundness test and alkali resistance test are conducted with the objective to further research the property changes of CGN-(F+S) grout. Density, surface hardness, water penetration capacity, water permeability capacity, soluble salt, scanning electron microscopy (SEM) images and energy dispersive spectrometry (EDS) spectrum of these samples have been tested after accelerated ageing tests. The results show that densities of samples decrease, surface hardness, water penetration capacity and water permeability capacity of samples increase generally. Besides, soluble salt analysis, SEM and EDS results well corroborate the changes. Based on the results it can be concluded that property changes are most serious after temperature and humidity cycling test, followed by water stability, soundness and alkali resistance test in sequence. But in general, CGN-(F+S) still has good durability.

Evaluation on High-temperature Adhesion Performance of Hot-applied Sealant for Asphalt Pavement

In order to investigate the high-temperature performances of the asphalt pavement hot-applied sealant, as well as to reduce failures of the sealant pullout, the softening point test and the flow test（two existing methods for evaluating high-temperature performances） were conducted. It was found that both tests could not accurately reflect the adhesion performances of the sealant at high temperatures. For this purpose, the adhesion test for PSAT（pressure sensitive adhesive tape） has been taken as a reference to develop a device that is suitable for evaluating the adhesion performances, by modifying relevant test parameters according to the road conditions at high temperatures. Thirteen common sealants were tested in the modified adhesion test, softening point test and f low test. The experimental results show that no significant correlation（p〉0.05） exists between the adhesion value, softening point, adhesion value and flow value; while a significant correlation（p〈0.05） exists between the softening point and flow value. The modified adhesion test is efficient in distinguishing the hightemperature adhesion performances of different sealants, and can be used as a standard method for evaluating such performances.

High-temperature Thermo-oxidative Aging of Vulcanized Natural Rubber Nanocomposites:Evolution of Microstructure and Mechanical Properties

The aging of natural rubber(NR)at high temperatures will seriously affect its service lifetime in many key applications.In the present work,the changes in microstructure and mechanical properties of semi-efficient vulcanized NR/carbon black(CB)vulcanizates during thermooxidative aging at high temperatures(150-200℃)and a moderate temperature(95℃)were compared.At high temperatures,a two-stage aging behavior,which was characteristic of a first rapid decline and then a continuous rise in the crosslinking density(ve),was identified and was found to be closely related to the depletion behavior of antioxidants.The surface cracking behavior observed in the second stage of high-temperature aging was discussed in terms of the grafting reaction of macromolecular radicals on CB particles and thermal expansion.In contrast,the aging of NR at moderate temperatures was much mild,which featured a continuous increase in ve and an oxidation mechanism dominated by peroxy radicals attacking double bonds.In general,the mechanical properties of NR vulcanizates during high-temperature aging depended on the competition effects of structural evolution in the crosslinked network and oxidation-induced chain scission.

High-temperature performance study of chromium-containing stuffing sand for ladles

High-temperature performance tests of chromium-containing stuffing sand for a steel ladle w ith different ratios w ere performed. A high-temperature simulation test furnace w as used to analyze the influence of the composition ratio of ladle filler sand and sintering time on the high-temperature compression resistance of chromium-containing stuffing sand in the temperature range of 1 500- 1 600 ℃. The results show that the refractoriness of ladle filler sand w as the low est（ only 1 610 ℃） w hen the composition ratio of chromite sand and silica sand w as 6∶ 4. M oreover,the high-temperature compression resistance w as high w hen the content of chromite sand w as at 70%; the resistance increased w ith increasing sintering time. When the sintering time w as extended at a temperature of 1 600 ℃,the high-temperature compression resistance of ladle filler sand first increased and then decreased after being overburnt.

An evaluation of OSOM BV blue test in the diagnosis of bacterial vaginosis

Objective:To determine the prevalence of bacterial vaginosis(BV) in patients with vaginal discharge and evaluate the efficacy of OSOM BV blue test in diagnosis.Methods:OSOM BV blue test,a rapid diagnostic test based on the principle of detection of bacterial sialidase activity in vaginal fluid specimens was conducted.A total of 405 patients in the reproductive age group(15- 45 years) having vaginal discharge were included in the study along with 10 healthy age-matched controls.Two high vaginal swabs were collected aseptically from each patient.One swab was used to make smear for gram staining,and the other was for OSOM BV blue test.Amine test and vaginal pH test were taken as well.Results:The prevalence of bacterial vaginosis was 60.7%. OSOM BV blue test showed good efficacy,as compared with gram staining in diagnosing BV.The sensitivity and specificity of OSOM BV blue test were 97.6%and 97.5%respectively.Amsel’s criteria diagnosed 180(44.4%) cases of BV and had sensitivity and specificity of 67.1%and 90.6%respectively.Thus the performance of OSOM BV blue was better than the methods based on Amsel’s criteria.Conclusions:OSOM BV blue test is an efficacious bed side test,helpful in rapidly making an accurate diagnosis of BV in setups lacking laboratory facilities or expert microbiologists.

Outdoor Aging Performance of HDPE Geogrid

An outdoor aging test base for geosynthetics was established in Wuhan,central China to investigate the long-term aging performance of geosynthetics. Outdoor photo-oxygen aging tests for high density polyethylene(HDPE) geogrid have been carried out in the base. Test results show that in the initial nine months,the tensile strength of geogrid remains unchanged or even gets larger,while the corresponding strain at break decreases slightly,exhibiting hard and brittle trend due to secondary compensatory responses to the ultraviolet(UV) aging: UV provides the required chemical crosslinking energy,resulting in the polymer crosslinking reaction. Tensile strength of the geogrid increases by about 5% in the initial nine months,but decreases after the initial nine months. The long-term research results at the test base could provide first-hand data for researching the aging properties of HDPE geogrid.

Surface destructive mechanism on high-temperature ablation, supersonic-erosion, dreg-adherence and corrosion

The exhaust and flame from a supersonic airborne missile high-energy smoke-born engine (SAMHSE) may lead to high-temperature ablation, supersonic-erosion, dreg-adherence (HTASED) and corrosion on the launcher slide track, causing serious problems to the operation and decreasing the lifetime of the launcher. Therefore, it is imperative to study the destructive mechanism so as to guarantee the smooth operation and increase the lifetime of military equipments. Accordingly, HTASED and corrosion were systematically observed and analyzed with the emphasis placed on the mechanism investigations making use of a series evaluation tests, typical missile engine simulation tests, national military standard methods, scanning electron microscopy and electrochemical corrosion tests. It is found that the thermal impact of high-temperature flame and supersonic erosion of corrosive melting particle jet of the SAMHSE lead to surface defects of micro-cracks, denudation and corrosive residue. Some defects reach to metal base becoming to "corrosive channels". Repetitive HTASED may cause ablation-adhesion fatigue stress, which enhances the surface corrosion and destruction. HTASED and corrosion are related to the type of a SAMHSE fuel and experience of the launcher. Surface destruction is related to synergistic effects of the HTASED. The ablated and failed Al or steel surface is liable to electrochemical corrosion characterized by pitting in humid and salt-spray environment.

Ex situ aging effect on sulfonated poly(ether ether ketone) membrane:Hydration-dehydration cycling and hydrothermal treatment

Prolonged hydrothermal treatment for sulfonated poly(ether ether ketone) membranes induces mechanical degradation and developing hydrophilic-hydrophobic phase separation, simultaneously. The enhanced phase separation provides incremental proton conductivity to the membranes, whereas mechanical degradation drastically reduces device stability. On this basis, we describe here the effects of two different ex situ aging processes on sulfonated poly(ether ether ketone) membranes: hydrationdehydration cycling and prolonged hydrothermal treatment. Both aged membranes exhibited enhanced phase separation under the hydrated conditions, as characterized by small angle X-ray scattering.However, when the aged membranes were dried again, the nanostructure of the membranes aged via the hydration-dehydration cycling was recoverable, whereas that of the membranes aged via prolonged hydrothermal treatment was irreversible. Furthermore, the two differently aged membranes showed clear differences in thermal, mechanical, and electrochemical properties. Finally, we implemented both aged membranes in fuel cell application. The sample aged via hydration-dehydration cycling maintained its improved cell performance, whereas the sample aged via hydrothermal treatment showed drastically reduced cell performance after durability test for 50 h.

Natural Ageing Tests to Study In-service Different Facade Solutions--ETICS and Premixed One-Coat Rendered Walls

In situ testing provides accurate characterization of existing degradation mechanisms of materials and building systems which helps reducing the subjectivity of visual inspections especially when ageing under natural ageing conditions is carried out over significant periods of time. In this work, data collected from field experimental campaigns over 10 years after construction using several premixed one-coat rendered walls and over 4 and 6 years after construction in the case of ETICS （external thermal insulation composite systems） are presented and discussed. The influence of hydrophobic agents on the performance of both types of facades in terms of surface condition and water penetration was assessed by visual inspections, Karsten test and capillary tests. Additionally, adhesion tests and subsequent evaluation of porosity were also carried out for premixed one-coat mortars. The results obtained have shown that ageing of the rendering solutions, especially after 5 or 6 years in-service, results from the loss of resistance to liquid water penetration, especially at the surface. Yet, additional mechanisms such as leaching of hydrophobic agents and photochemical degradation are thought to be involved, too. Moreover, the results obtained using the Karsten test proved to be the most reliable method to determine the loss of water penetration resistance and predict the ageing of facade solutions. The information collected and the correlations established can help developing solutions to prevent early ageing and implement appropriate maintenance plans to delay their effect.