Serpentinization produces molecular hydrogen(H2)that can support communities of microorganisms in hydrothermal fields;H2 results from the oxidation of ferrous iron in olivine and pyroxene into ferric iron,and conseque...Serpentinization produces molecular hydrogen(H2)that can support communities of microorganisms in hydrothermal fields;H2 results from the oxidation of ferrous iron in olivine and pyroxene into ferric iron,and consequently iron oxide(magnetite or hematite)forms.However,the mechanisms that control H2 and iron oxide formation are poorly constrained.In this study,we performed serpentinization experiments at 311℃ and 3.0 kbar on olivine(with <5% pyroxene),orthopyroxene,and peridotite.The results show that serpentine and iron oxide formed when olivine and orthopyroxene individually reacted with a saline starting solution.Olivine-derived serpentine had a significantly lower FeO content(6.57±1.30 wt.%)than primary olivine(9.86 wt.%),whereas orthopyroxene-derived serpentine had a comparable FeO content(6.26±0.58 wt.%)to that of primary orthopyroxene(6.24 wt.%).In experiments on peridotite,olivine was replaced by serpentine and iron oxide.However,pyroxene transformed solely to serpentine.After 20 days,olivine-derived serpentine had a FeO content of 8.18±1.56 wt.%,which was significantly higher than that of serpentine produced in olivine-only experiments.By contrast,serpentine after orthopyroxene had a slightly higher FeO content(6.53±1.01 wt.%)than primary orthopyroxene.Clinopyroxene-derived serpentine contained a significantly higher FeO content than its parent mineral.After 120 days,the FeO content of olivine-derived serpentine decreased significantly(5.71±0.35 wt.%),whereas the FeO content of orthopyroxene-derived serpentine increased(6.85±0.63 wt.%)over the same period.This suggests that iron oxide preferentially formed after olivine serpentinization.Pyroxene in peridotite gained some Fe from olivine during the serpentinization process,which may have led to a decrease in iron oxide production.The correlation between FeO content and SiO_2 or AI_2 O_3 content in olivine-and orthopyroxene-derived serpentine indicates that aluminum and silica greatly control the production of iron oxide.Based on our results and data from natural serpentinites reported by other workers,we propose that aluminum may be more influential at the early stages of peridotite serpentinization when the production of iron oxide is very low,whereas silica may have a greater control on iron oxide production during the late stages instead.展开更多
Magnetic signature of serpentinized mantle peridotite has crucial importance in understanding the serpentinization process and interpreting the origin of strong magnetization anomalies at ultramafic-hosted hydrotherma...Magnetic signature of serpentinized mantle peridotite has crucial importance in understanding the serpentinization process and interpreting the origin of strong magnetization anomalies at ultramafic-hosted hydrothermal settings. However, different groups of serpentinized peridotites from both ocean drillings and ophiolite complexes have shown considerable variations in the abundance of magnetite(Oufi et al., 2002;Bonnemains et al., 2016;Li et al., 2017). We examined the magnetic properties, petrography and mineral chemistry of variably serpentinized peridotites from Zedang ophiolite in the eastern Yarlung-Zangbo suture in south Tibet to evaluate the conditions of serpentinization and magnetite formation as well as magnetic sources in suture zones. The studied samples were 0–90% serpentinized with densities from 3.316 to 2.593 g cm–3 and show typical mesh textures of olivine replaced by serpentine on thin sections of core specimen. Serpentines were divided into type-1 Fe-poor serpentine mesh(1.84–2.88 wt% FeO) associated with magnetite in the early stage and type-2 Fe-rich serpentine cores(3.92–5.12 wt% FeO) with no formation of magnetite in the late serpentinization. Brucite vein appeared in central serpentine veins and show Mg/(Mg+Fe) values of 0.74–0.87 at ~50–70% of serpentinization. Pure magnetite was identified as the main magnetic carrier by thermomagnetic analyses, but minor Cr-magnetite(~0.8 mole fractions of Fe3O4) was also detected due to oxidation of early spinel. All the peridotite samples show a rapid increase of magnetic susceptibility from ~0.001 to ~0.03 SI before 40–50% of serpentinization and a following flat trend in values 0.02–0.03 SI at > 50% of serpentinization. This density-susceptibility relationship differs from the rapid production of magnetite above 60-70% of serpentinization for many abyssal peridotites(Oufi et al., 2002;Bach et al., 2006) and suggests that magnetite formation was coupled with hydration of olivine in the early serpentinization but the two decoupled at ~ 40–50% of serpentinization. This transition is consistent with the petrographic observation that magnetite-free serpentinization was developed in higher degrees(> 50%) of serpentinization. Prior studies suggested that serpentinization of < 200℃ would generate Fe-rich brucite, serpentine and little magnetite, whereas magnetite-rich serpentinization was associated with Fe-poor brucite and occurred at higher temperatures of 200–300℃(Klein et al., 2014). The petromagnetic features of serpentinized peridotites from the Zedang ophiolite indicate that the serpentinization process took place initially above 250℃(estimate from brucite composition) and continued to lower temperatures of < 200℃, probably during the mantle lithosphere cooling down in forearc settings(Xiong et al., 2017). These serpentinized peridotites have higher magnetization intensities(average 2.26 Am-1) than mafic dolerite dykes and basaltic volcanic rocks(mostly < 1 Am-1) and should be significant sources of aeromagnetic highs in the Yarlung-Zangbo suture.展开更多
Serpentinization reactions are paramount to understand hydro-geothermal activity near plate boundaries and mafic–ultramafic massifs,as well as fluid and element transfer between the Earth’s mantle and crust.However,...Serpentinization reactions are paramount to understand hydro-geothermal activity near plate boundaries and mafic–ultramafic massifs,as well as fluid and element transfer between the Earth’s mantle and crust.However,fluid-rock element exchange and serpentinization kinetics under shallow hydrothermal conditions is still largely unconstrained.Here we present two constant temperature(230℃)time-series of natural peridotite(77.5%olivine;13.7%enstatite;6.8%diopside;2%spinel)serpentinization experiments:at 13.4 MPa;and 20.7 MPa.Al-enriched lizardite was the main secondary mineral in all runs after olivine(olv)and orthopyroxene(opx)serpentinization(without any detectable brucite,talc or magnetite),while primary spinel and diopside partially dissolved during the experiments.Initial serpentinization stages comprises intrinsically coupled reactions between olivine and enstatite,as Al and Si are progressively transferred from orthopyroxene-derived to olivine-derived serpentine,while the opposite is true for Mg and Fe,with homogenization of serpentines compositions after 40 days.The Ni/Cr ratios of serpentines,however,remain diagnostic of the respective primary mineral.Estimated average serpentine content indicates fast serpentinization rates of 0.55 wt.%·day^(-1)(0.26 mmol·day^(-1))and 0.26 wt.%·day^(-1)(0.13 mmol·day^(-1))at 13.4 and 20.7 MPa,respectively.Approximately 2x faster serpentinization kinetics at lower pressure is likely linked to enhanced spinel dissolution leading to one order of magnitude higher available Al,which accelerates olivine serpentinization while delays orthopyroxene dissolution.Additionally,time-dependent increase in solid products masses suggests rock volume expands linearly 0.37%±0.01%per serpentine wt.%independently of pressure.Mass balance constrains suggests olv:opx react at~5:2 and~3:2 M ratios,resulting in Si-deficient and Si-saturated serpentines at the end of the low-pressure series(13.4 MPa)and high-pressure series(20.7 MPa),respectively.Elevated starting peridotite olv:opx ratio(7.94:1)therefore indicates orthopyroxene serpentinization is~3.3x and~5.4x faster than olivine at 13.4 MPa and 20.7 MPa,respectively.This contradicts previous assumptions that olivine should dissolve faster than orthopyroxene at experimental conditions.Finally,serpentinization-derived fluids develop pH>10 and become enriched in H_(2),CH_(4),Ca^(2+)and Si within 6 weeks.Aqueous silica concentrations are highest after 5 days(265.75 and 194.79µmol/kg)and progressively decrease,reaching 13.84 and 91.54µmol/kg at 13.4 and 20.7 MPa after 40 days,respectively.These concentrations are very similar to the low-silica(M6)and high-silica(Beehive)endmembers of the Lost City Hydrothermal Field(LCHF).Beyond fluid characteristics,serpentinization products and conditions analogous to the LCHF suggest similar mechanisms between our experiments and natural processes.Our results demonstrate constant temperature serpentinization of a common protolith leads to distinct serpentine and fluid compositions at different pressures.Although additional data is necessary,recent studies and our experiments suggest peridotite serpentinization rates at 230℃rapidly decrease with increasing pressures at least up to 35 MPa.Whether pressure directly influences olivine and orthopyroxene serpentinization kinetics or indirectly controls reaction rates due to spinel dissolution under hydrothermal conditions deserves further investigation.展开更多
The dependence of starting materials and their initial grain sizes on the formation of gases （H2, CH4, C2H6 and C3Hs） during serpentinization was investigated by conducting hydrothermal experiments at 311℃ and 3 kb...The dependence of starting materials and their initial grain sizes on the formation of gases （H2, CH4, C2H6 and C3Hs） during serpentinization was investigated by conducting hydrothermal experiments at 311℃ and 3 kbar on olivine and peridotite with initial grain sizes ranging from 〈30 to 177 μm. Hydrocarbons （CH4, C2H6 and C3H8） were produced from reaction between dissolved CO2 in the starting fluids and HE formed during serpentinization, which were analyzed by Gas Chromatography. It was found that olivine serpentinization produced much less H2 and CH4 compared with those after peridotite alteration, while their C2H6 and C3H8 were identical. For example, for olivine with initial grain sizes of 〈30 μm, the amounts of HE and CH4 were 79.6 mmol/kg and 460 μmol/kg after 27 days, respectively. By contrast, the quantities of H2 and CH4 produced in experiment on peridotite with the same run duration were much larger, 119 mmol/kg and 1300 μmol/kg, respectively. This indicates that spinel and pyroxene in peridotite may increase the amounts of HE and hydrocarbons, possibly due to the catalytic effect of aluminum released by spinel and pyroxene during serpentinization. Moreover, the production of H2 and hydrocarbons is negatively correlated with initial grain sizes of the starting material, with smaller amounts of HE and hydrocarbons for larger initial grain sizes, indicating that the kinetics of serpentinization influences the formation of HE and hydrocarbons, possibly because of the lack of catalytic minerals for the starting material with larger grain sizes. This study suggests that olivine cannot completely represent peridotite during serpentinization, and that H2 and hydrocarbons in hydrothermal fields near the mid-ocean ridge may be produced in a very long period of serpentinization or the presence of catalytic minerals due to large grain sizes of ultramafic rocks.展开更多
Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology.In this study,magnesium silicate hydroxide(MSH)nanotubes with serpentine structures were synthesized.The tribological b...Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology.In this study,magnesium silicate hydroxide(MSH)nanotubes with serpentine structures were synthesized.The tribological behavior of AZ91D magnesium alloy rubbed against GCr15 steel was studied under lubricating oil with surface-modified MSH nanotubes as additives.The effects of the concentration,applied load,and reciprocating frequency on the friction and wear of the AZ91D alloy were studied using an SRV-4 sliding wear tester.Results show a decrease of 18.7–68.5%in friction coefficient,and a reduction of 19.4–54.3%in wear volume of magnesium alloy can be achieved by applying the synthetic serpentine additive under different conditions.A suspension containing 0.3 wt.%MSH was most efficient in reducing wear and friction.High frequency and medium load were more conducive to improving the tribological properties of magnesium alloys.A series of beneficial physical and chemical processes occurring at the AZ91D alloy/steel interface can be used to explain friction and wear reduction based on the characterization of the morphology,chemical composition,chemical state,microstructure,and nanomechanical properties of the worn surface.The synthetic MSH,with serpentine structure and nanotube morphology,possesses excellent adsorbability,high chemical activity,and good self-lubrication and catalytic activity.Therefore,physical polishing,tribochemical reactions,and physicalchemical depositions can occur easily on the sliding contacts.A dense tribolayer with a complex composition and composite structure was formed on the worn surface.Its high hardness,good toughness and plasticity,and prominent lubricity resulted in the improvement of friction and wear,making the synthetic MSH a promising efficient oil additive for magnesium alloys under boundary and mixed lubrication.展开更多
The resource-intensive,high-fidelity infrared signature simulations and Radar CrossSection(RCS)calculations limit the integrated optimization of Unmanned Combat Aerial Vehicles(UCAVs)in response to escalating threats ...The resource-intensive,high-fidelity infrared signature simulations and Radar CrossSection(RCS)calculations limit the integrated optimization of Unmanned Combat Aerial Vehicles(UCAVs)in response to escalating threats from joint detection systems.To this end,we present a sample-efficient framework to advance the optimization efficiency of UCAV's exhaust system,focusing on both the stealth characteristics evaluation and the optimization process.A novel multi-fidelity stealth assessment method,powered by multi-fidelity neural network and local perceptive fields,has been developed to fuse different fidelity information from infrared radiation signature and RCS values,respectively.Results demonstrate that the method can achieve relatively high accuracy based on a small set of high-fidelity data.Furthermore,this data fusion method is integrated into a multi-objective Bayesian optimization framework.Employing a Gaussian process regression model and the EHVI acquisition function,the framework effectively explores the stealth objective space,achieving a 15.21%hypervolume indicator increase with fewer optimization iterations compared to NSGA-Ⅱ.Results show that the optimized nozzle significantly reduces both the infrared signature and RCS compared to the baseline configuration.The proposed framework offers a practical and efficient approach for optimizing the integrated stealth performance of UCAVs.展开更多
Serpentine structured Co_(3)Si_(2)O_(5)(OH)_(4) is inexpensive,chemically stable,and electrochemically active in oxygen evolution reactions(OER).However,the OER activity of Co_(3)Si_(2)O_(5)(OH)_(4) materials is still...Serpentine structured Co_(3)Si_(2)O_(5)(OH)_(4) is inexpensive,chemically stable,and electrochemically active in oxygen evolution reactions(OER).However,the OER activity of Co_(3)Si_(2)O_(5)(OH)_(4) materials is still unfavorable due to the low active sites.Here,Mn^(2+)-doped Co_(3)Si_(2)O_(5)(OH)_(4) serpentine nanosheets with tuned d-band centers are achieved for efficient oxygen evolution in alkaline and neutral electrolytes.The Co_(x)Mn_(3−x)Si_(2)O_(5)(OH)_(4) serpentine nanosheets are synthesized by a simple hydrothermal method.The optimized Co_(2.4)Mn_(0.6)Si_(2)O_(5)(OH)_(4) serpentine nanosheets showed favorable OER overpotentials as well as stable durability in KOH solution and phosphate buffer solution,which were superior to most of the Co-based and Mn-based OER electrocatalysts.The in situ Raman spectroscopy shows that the materials are kept well in the electrochemical OER environments.Further density functional theory shows that the d-band center of Co_(x)Mn_(3−x)Si_(2)O_(5)(OH)_(4) serpentine nanosheets is shifted more upward in comparison with pristine Co_(3)Si_(2)O_(5)(OH)_(4).The changes in the d-band center increase the adsorption of intermediates,optimize the reaction steps,and lower the energy barriers of the OER.That is the main reason for the OER enhancement Mn^(2+)-doped Co_(3)Si_(2)O_(5)(OH)_(4).This work gives an efficient strategy to design cheap and stable electrocatalytic materials for OER in a broad pH environment.展开更多
The serpentine convergent-divergent nozzle represents an optimal configuration for nextgeneration fighter aircraft characterized by low detectability and high thrust-to-weight ratio.In contrast to the serpentine conve...The serpentine convergent-divergent nozzle represents an optimal configuration for nextgeneration fighter aircraft characterized by low detectability and high thrust-to-weight ratio.In contrast to the serpentine convergent nozzle,such configuration offers increased design flexibility with additional parameters,leading to heightened interactions among these parameters.As such,it is crucial to reveal the influence of design parameters on the aerodynamic performance of the serpentine convergent-divergent nozzle and the multifactor interaction,as well as its mechanism.Therefore,the influence,interaction and sensitivity of parameters on the aerodynamic performance of the nozzle were numerically investigated using the orthogonal test method.Additionally,the influence mechanism of the convergence angle,throat aspect ratio,and axial length to inlet diameter on the flow characteristics of the nozzle was investigated in detail.The results show that the convergence angle is identified as the main factor affecting the aerodynamic parameters of the nozzle.As the convergence angle increases,the thrust coefficient,total pressure recovery coefficient and discharge coefficient gradually decrease.The interaction between throat aspect ratio and other parameters is obvious.Different design parameters affect the local loss and the friction loss by affecting the curvature and wetted perimeter area,resulting in different aerodynamic characteristics of serpentine convergent-divergent nozzle.展开更多
Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydro...Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydrous uvarovite garnet having Cr_(2)O_(3) upto 19.66 wt% and CaO of 32.12–35.14 wt% in the serpentinized mantle peridotites of Naga Hills Ophiolite(NHO), India. They occur in association with low-Cr diopsides. They are enriched in LILE(Ba, Sr), LREEs, with fractionating LREE-MREE [avg.(La/Sm)_(N) = 2.16] with flat MREE/HREE patterns [avg.(Sm/Yb)_(N) = 0.95]. Raman spectra indicate the presence of hydroxyl(OH^(–)) peaks from 3500 to 3700 cm^(-1). Relative abundances in fluid mobile elements and their close association with clinopyroxenes are suggestive of the formation of uvarovite garnets through low temperature metasomatic alteration of low-Cr diopsides by hydrothermal slab fluids. The high LREE concentration and absence of Eu anomaly in the garnet further attest to alkaline nature of the transporting slab dehydrated fluid rather the involvement of low-p H solution. The chemical characteristics of the hydroxyl bearing uvarovite hosted by the mantle peridotite of NHO deviate from the classical features of uvarovite garnet, and their origin is attributed to the fluid-induced metasomatism of the sub arc mantle wedge in a suprasubduction zone regime.展开更多
The produced water from the oilfield was purified with filter material and then injected back into the ground.The serpentine filter material was easy to harden with the increase in filtration amount,which affected the...The produced water from the oilfield was purified with filter material and then injected back into the ground.The serpentine filter material was easy to harden with the increase in filtration amount,which affected the water quality.A superhydrophilic/underwater oleophobic serpentine filter material was successfully prepared by a simple method of coating modification,which exhibited long-lasting filtration of oily water,good filtration and anti-fouling properties,and resistance to harden.The film-forming material of the superhydrophilic/underwater oleophobic coating was composed of SiO_(2) particles with small size,which could completely and evenly cover the filter particle.The weight loss was only 7.6%after mechanical stirring for 90 min.Compared with the original filter material,the superhydrophilic/underwater oleophobic serpentine filter material showed a better anti-fouling ability and resistance to harden.The filtration of crude oil emulsion and oil slick sewage showed a better backwashing performance.After 35 cycles of continuous filtration of suspended solids in wastewater,the backwashing rate reached 78.4%.The results provided an effective method for the filtration of oily wastewater in the oilfield.展开更多
The high-efficiency Shock Vectoring Control Serpentine Nozzle(SVCSN)takes into account both thrust vectoring and infrared stealth,and significantly improves the comprehensive performance of the aero-engines through an...The high-efficiency Shock Vectoring Control Serpentine Nozzle(SVCSN)takes into account both thrust vectoring and infrared stealth,and significantly improves the comprehensive performance of the aero-engines through an additional auxiliary duct.In this paper,the schlieren photographs at the exit of the high-efficiency SVCSN and the wall static pressure distributions were obtained by experiments,and the numerical results were used to enrich the thrust vectoring characteristics.The effects of the auxiliary injection were analyzed first to reveal the advantages of the high-efficiency SVCSN compared to the conventional SVCSN.Then,the aerodynamic parameters and the structural parameters of the high-efficiency SVCSN were investigated,including the Nozzle Pressure Ratio(NPR),the Secondary flow Pressure Ratio(SPR),the secondary flow relative area and the secondary flow injection angle.Finally,the coupling performance of the high-efficiency SVCSN is studied by using the approximate modeling technology.Results show that the auxiliary injection increases the range between the two shock legs of the “k”shock wave induced by the secondary flow,then causes the separation zone and high-pressure boss of the down wall to expand upstream,and finally results in a prominent increase in the thrust vectoring performance.The thrust vectoring angle and Vectoring Efficiency(VE)of the high-efficiency SVCSN are about 61.6%and 75.7%,respectively,higher than those of the conventional SVCSN at NPR=6.The effects of the NPR and the SPR on the thrust vectoring performance of the high-efficiency SVCSN are coupled with each other.A larger NPR matched with a smaller SPR shows better thrust vectoring performance.The maximum fluctuations in thrust vectoring angle and VE caused by the NPR and SPR are about 22%and 64%.The VE decreases monotonously with the increase of the secondary flow relative area.Smaller secondary flow injection angle shows better thrust vector performance,and the thrust vectoring angle and VE of the secondary flow injection angle of 90are about 20%higher than those of the secondary flow injection angle of 110at NPR=6.Therefore,the secondary flow relative area of 0.06 and the secondary flow injection angle of 90are recommended.展开更多
The effect of sodium hexametaphosphate（SHMP） on the separation of serpentine from pyrite and its mechanism were studied systematically through flotation tests,sedimentation tests,surface dissolution,ζ potential tes...The effect of sodium hexametaphosphate（SHMP） on the separation of serpentine from pyrite and its mechanism were studied systematically through flotation tests,sedimentation tests,surface dissolution,ζ potential tests,adsorption measurements,and infrared spectroscopic analyses.The results show that the SHMP could significantly reduce the adverse effect of serpentine on the flotation of pyrite and make the mixed sample of pyrite and serpentine more disperse in the alkaline condition,thus improve the adsorption of xanthate on pyrite.The action mechanism of the SHMP is that it lowers the pH value at the isoelectric point of serpentine and enhances the negative charge through the dissolution of magnesium from the surface of serpentine and adsorbing on the surface of serpentine.It changes the total interaction energy between serpentine and pyrite from gravitational potential energy to repulse potential energy,according to the calculation of the EDLVO theory.展开更多
The electrokinetic behavior and surface dissolution of serpentine mineral were studied through Zeta potential measurements, dissolution experiments and X-ray photoelectron spectroscopy. The results show that serpentin...The electrokinetic behavior and surface dissolution of serpentine mineral were studied through Zeta potential measurements, dissolution experiments and X-ray photoelectron spectroscopy. The results show that serpentine has an iso-electric point （IEP） of 11.9, which is higher than that of other phyllosilicate minerals. Dissolution experiments show that the hydroxyl is easy to dissolve with respect to the magnesium cations in the magnesium oxide octahedral sheet. As a result of hydroxyl dissolution, the magnesium ions are left on serpentine surface, which is responsible for serpentine surface charge. The removal of magnesium ions from serpentine surface by acid leaching results in a decrease of serpentine IEP. Therefore, it has been clearly established that the surface charge developed at the serpentine/aqueous electrical interface is a function of the serpentine surface incongruent dissolution.展开更多
An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process （SCRC）,was explored.The mechanical properties and microstructures of the tensile samples...An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process （SCRC）,was explored.The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions.The experimental results show that the as-cast ultimate tensile strength can reach about 250MPa and the elongation is 8.6%？13.2%.The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment.Under these experimental conditions,the semi-solid A356 Al alloy slurry with primary α1（Al） grains,which have the shape factor of 0.78？0.89 and the grain diameter of 35？45μm,can be prepared by the serpentine channel pouring process.The primary α2（Al） grains are very fine during the secondary solidification stage.Compared with the conventional HPDC process,the SCRC process can improve the microstructures and mechanical properties of the tensile test samples.The advantages of the SCRC process include easily incorporating with an existing HPDC machine,cancelling the preservation and transportation process of the semi-solid alloy slurry,and a higher cost performance.展开更多
The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel （SCP）. Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were i...The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel （SCP）. Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were investigated. The results demonstrated that the semi-solid 7075 aluminum alloy slurry with satisfied quality could be generated by a serpentine pouring channel when the pouring temperature was in the range of 680-700 ℃. At a given pouring temperature, the equivalent size of the primaryα（Al） grains decreased and the shape factor increased with the increase of the number of turns. During the slurry preparation of semi-solid 7075 aluminum alloy, the flow direction of alloy melt changed many times when it flowed in a curved and closed serpentine channel. With the effect of“stirring”in it , the primary nuclei gradually evolved into spherical and near-spherical grains.展开更多
The integral microstructure of semisolid A356 alloy slurry with larger capacity cast by serpentine channel was studied and the influence of cooling ability of serpentine channel on the microstructure was investigated....The integral microstructure of semisolid A356 alloy slurry with larger capacity cast by serpentine channel was studied and the influence of cooling ability of serpentine channel on the microstructure was investigated. The results indicate that ideal slurry with larger capacity can be prepared through serpentine channel with good cooling ability. When the serpentine channel was continuously cooled, both the longitudinal and the radial microstructure of the slurry was composed of granular primary phase and the integral microstructure uniformity of the slurry was good. However, uncooled serpentine channel can only produce larger slurry with fine grains in positions adjacent to its centre and with a large number of dendrites in positions close to its edge, thus, the radial microstructure of larger slurry is nonuniform. The pouring temperature is set up to 680 °C and the solid shell inside the channel can be avoided at this pouring temperature.展开更多
The magnetism of pentlandite surface was enhanced through the selective precipitation of micro-fine magnetite fractions on pentlandite surfaces. This was achieved through adjustment of slurry pH and addition of surfac...The magnetism of pentlandite surface was enhanced through the selective precipitation of micro-fine magnetite fractions on pentlandite surfaces. This was achieved through adjustment of slurry pH and addition of surfactants. The results showed that at pH 8.8 with the addition of 100 g/t sodium hexametaphosphate, 4.5 L/t oleic acid, and 4.5 L/t kerosene, significant amount of fine magnetite particles adhered to the pentlandite surface, while trace amount of coating was found on serpentine surfaces. Thus, the magnetism of pentlandite was enhanced and pentlandite was well separated from serpentine by magnetic separation under the magnetic field intensity of 200 kA/m. Scanning electron microscopy （SEM） and zeta potential measurement were performed to characterize changes of mineral surface properties. Calculations of the extended Derjaguin-Landau-Verwey-Ocerbeek （EDLVO） theory indicated that, in the presence of surfactants the total interaction energy between magnetite and pentlandite became stronger than that between magnetite and serpentine. This enabled the selective adhesion of magnetite particles to pentlandite surfaces, thereby enhancing its magnetism.展开更多
The semi-solid slurry of A380 aluminum alloy was prepared by the serpentine channel. The effects of pouring temperature, curve number and curve diameter of the serpentine channel on the microstructure of the semi-soli...The semi-solid slurry of A380 aluminum alloy was prepared by the serpentine channel. The effects of pouring temperature, curve number and curve diameter of the serpentine channel on the microstructure of the semi-solid A380 aluminum alloy slurry were investigated. The results show that the satisfactory semi-solid A380 aluminum alloy slurry could be obtained when the pouring temperature ranged from 630 to 650 °C. Under the same conditions, increasing the curve number or reducing the curve diameter of the serpentine channel would decrease the average diameter and increase the shape factor of the primary α（Al） grains. The ＂self-stirring＂ of the alloy melt in the serpentine channel was beneficial to the ripening of the dendrites and the spheroidizing of the primary α（Al） grains.展开更多
Semi-solid A356 aluminum alloy slurry was prepared by using serpentine channel pouring process, and the influences of the channel diameters and pouring temperatures on the semi-solid A356 aluminum alloy slurry were in...Semi-solid A356 aluminum alloy slurry was prepared by using serpentine channel pouring process, and the influences of the channel diameters and pouring temperatures on the semi-solid A356 aluminum alloy slurry were investigated. The experimental results show that when the channel diameter is 20 and 25 mm, respectively, and the pouring temperature is 640-680 ℃, the average diameter of primary α（Al） grains in the prepared A356 aluminum alloy slurry is 50-75 and 55-78 μm, respectively, and the average shape factor of primary α（Al） grains is 0.89-0.76 and 0.86-0.72, respectively. With the decline in the pouring temperature, the microstructure of semi-solid A356 aluminum alloy slurry is more desirable and a serpentine channel with smaller diameter is also advantageous to the microstructure imProvement. During the preparation of semi-solid A356 aluminum alloy slurry, a large number of nuclei can be produced by the chilling effect of the serpentine channel, and owing to the combined effect of the chilled nuclei separation and melt self-stirring, primary α（Al） nuclei can be multiplied and spheroidized finally.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.41603060,91328204)Postdoctoral Science Foundation of China(Nos.2015M570735,2016T90805)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB06030100)the scientific research fund of the Second Institute of Oceanography,SOA(JG1405)
文摘Serpentinization produces molecular hydrogen(H2)that can support communities of microorganisms in hydrothermal fields;H2 results from the oxidation of ferrous iron in olivine and pyroxene into ferric iron,and consequently iron oxide(magnetite or hematite)forms.However,the mechanisms that control H2 and iron oxide formation are poorly constrained.In this study,we performed serpentinization experiments at 311℃ and 3.0 kbar on olivine(with <5% pyroxene),orthopyroxene,and peridotite.The results show that serpentine and iron oxide formed when olivine and orthopyroxene individually reacted with a saline starting solution.Olivine-derived serpentine had a significantly lower FeO content(6.57±1.30 wt.%)than primary olivine(9.86 wt.%),whereas orthopyroxene-derived serpentine had a comparable FeO content(6.26±0.58 wt.%)to that of primary orthopyroxene(6.24 wt.%).In experiments on peridotite,olivine was replaced by serpentine and iron oxide.However,pyroxene transformed solely to serpentine.After 20 days,olivine-derived serpentine had a FeO content of 8.18±1.56 wt.%,which was significantly higher than that of serpentine produced in olivine-only experiments.By contrast,serpentine after orthopyroxene had a slightly higher FeO content(6.53±1.01 wt.%)than primary orthopyroxene.Clinopyroxene-derived serpentine contained a significantly higher FeO content than its parent mineral.After 120 days,the FeO content of olivine-derived serpentine decreased significantly(5.71±0.35 wt.%),whereas the FeO content of orthopyroxene-derived serpentine increased(6.85±0.63 wt.%)over the same period.This suggests that iron oxide preferentially formed after olivine serpentinization.Pyroxene in peridotite gained some Fe from olivine during the serpentinization process,which may have led to a decrease in iron oxide production.The correlation between FeO content and SiO_2 or AI_2 O_3 content in olivine-and orthopyroxene-derived serpentine indicates that aluminum and silica greatly control the production of iron oxide.Based on our results and data from natural serpentinites reported by other workers,we propose that aluminum may be more influential at the early stages of peridotite serpentinization when the production of iron oxide is very low,whereas silica may have a greater control on iron oxide production during the late stages instead.
基金granted by the Fundamental Research Funds for the Central Universities (Grant No. CUG180620)the NSFC project (Grant No. 41520104003)
文摘Magnetic signature of serpentinized mantle peridotite has crucial importance in understanding the serpentinization process and interpreting the origin of strong magnetization anomalies at ultramafic-hosted hydrothermal settings. However, different groups of serpentinized peridotites from both ocean drillings and ophiolite complexes have shown considerable variations in the abundance of magnetite(Oufi et al., 2002;Bonnemains et al., 2016;Li et al., 2017). We examined the magnetic properties, petrography and mineral chemistry of variably serpentinized peridotites from Zedang ophiolite in the eastern Yarlung-Zangbo suture in south Tibet to evaluate the conditions of serpentinization and magnetite formation as well as magnetic sources in suture zones. The studied samples were 0–90% serpentinized with densities from 3.316 to 2.593 g cm–3 and show typical mesh textures of olivine replaced by serpentine on thin sections of core specimen. Serpentines were divided into type-1 Fe-poor serpentine mesh(1.84–2.88 wt% FeO) associated with magnetite in the early stage and type-2 Fe-rich serpentine cores(3.92–5.12 wt% FeO) with no formation of magnetite in the late serpentinization. Brucite vein appeared in central serpentine veins and show Mg/(Mg+Fe) values of 0.74–0.87 at ~50–70% of serpentinization. Pure magnetite was identified as the main magnetic carrier by thermomagnetic analyses, but minor Cr-magnetite(~0.8 mole fractions of Fe3O4) was also detected due to oxidation of early spinel. All the peridotite samples show a rapid increase of magnetic susceptibility from ~0.001 to ~0.03 SI before 40–50% of serpentinization and a following flat trend in values 0.02–0.03 SI at > 50% of serpentinization. This density-susceptibility relationship differs from the rapid production of magnetite above 60-70% of serpentinization for many abyssal peridotites(Oufi et al., 2002;Bach et al., 2006) and suggests that magnetite formation was coupled with hydration of olivine in the early serpentinization but the two decoupled at ~ 40–50% of serpentinization. This transition is consistent with the petrographic observation that magnetite-free serpentinization was developed in higher degrees(> 50%) of serpentinization. Prior studies suggested that serpentinization of < 200℃ would generate Fe-rich brucite, serpentine and little magnetite, whereas magnetite-rich serpentinization was associated with Fe-poor brucite and occurred at higher temperatures of 200–300℃(Klein et al., 2014). The petromagnetic features of serpentinized peridotites from the Zedang ophiolite indicate that the serpentinization process took place initially above 250℃(estimate from brucite composition) and continued to lower temperatures of < 200℃, probably during the mantle lithosphere cooling down in forearc settings(Xiong et al., 2017). These serpentinized peridotites have higher magnetization intensities(average 2.26 Am-1) than mafic dolerite dykes and basaltic volcanic rocks(mostly < 1 Am-1) and should be significant sources of aeromagnetic highs in the Yarlung-Zangbo suture.
基金We thank Petrobras for sponsoring the grad studies of the main author and its financial support through project 8310-0 FAURGS-UFRGS-PETROBRAS.
文摘Serpentinization reactions are paramount to understand hydro-geothermal activity near plate boundaries and mafic–ultramafic massifs,as well as fluid and element transfer between the Earth’s mantle and crust.However,fluid-rock element exchange and serpentinization kinetics under shallow hydrothermal conditions is still largely unconstrained.Here we present two constant temperature(230℃)time-series of natural peridotite(77.5%olivine;13.7%enstatite;6.8%diopside;2%spinel)serpentinization experiments:at 13.4 MPa;and 20.7 MPa.Al-enriched lizardite was the main secondary mineral in all runs after olivine(olv)and orthopyroxene(opx)serpentinization(without any detectable brucite,talc or magnetite),while primary spinel and diopside partially dissolved during the experiments.Initial serpentinization stages comprises intrinsically coupled reactions between olivine and enstatite,as Al and Si are progressively transferred from orthopyroxene-derived to olivine-derived serpentine,while the opposite is true for Mg and Fe,with homogenization of serpentines compositions after 40 days.The Ni/Cr ratios of serpentines,however,remain diagnostic of the respective primary mineral.Estimated average serpentine content indicates fast serpentinization rates of 0.55 wt.%·day^(-1)(0.26 mmol·day^(-1))and 0.26 wt.%·day^(-1)(0.13 mmol·day^(-1))at 13.4 and 20.7 MPa,respectively.Approximately 2x faster serpentinization kinetics at lower pressure is likely linked to enhanced spinel dissolution leading to one order of magnitude higher available Al,which accelerates olivine serpentinization while delays orthopyroxene dissolution.Additionally,time-dependent increase in solid products masses suggests rock volume expands linearly 0.37%±0.01%per serpentine wt.%independently of pressure.Mass balance constrains suggests olv:opx react at~5:2 and~3:2 M ratios,resulting in Si-deficient and Si-saturated serpentines at the end of the low-pressure series(13.4 MPa)and high-pressure series(20.7 MPa),respectively.Elevated starting peridotite olv:opx ratio(7.94:1)therefore indicates orthopyroxene serpentinization is~3.3x and~5.4x faster than olivine at 13.4 MPa and 20.7 MPa,respectively.This contradicts previous assumptions that olivine should dissolve faster than orthopyroxene at experimental conditions.Finally,serpentinization-derived fluids develop pH>10 and become enriched in H_(2),CH_(4),Ca^(2+)and Si within 6 weeks.Aqueous silica concentrations are highest after 5 days(265.75 and 194.79µmol/kg)and progressively decrease,reaching 13.84 and 91.54µmol/kg at 13.4 and 20.7 MPa after 40 days,respectively.These concentrations are very similar to the low-silica(M6)and high-silica(Beehive)endmembers of the Lost City Hydrothermal Field(LCHF).Beyond fluid characteristics,serpentinization products and conditions analogous to the LCHF suggest similar mechanisms between our experiments and natural processes.Our results demonstrate constant temperature serpentinization of a common protolith leads to distinct serpentine and fluid compositions at different pressures.Although additional data is necessary,recent studies and our experiments suggest peridotite serpentinization rates at 230℃rapidly decrease with increasing pressures at least up to 35 MPa.Whether pressure directly influences olivine and orthopyroxene serpentinization kinetics or indirectly controls reaction rates due to spinel dissolution under hydrothermal conditions deserves further investigation.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.4109037341121002+2 种基金41103012 and 41173069)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB06030100)also by Postdoctoral Science Foundation of China(Grant No.2015M570735)
文摘The dependence of starting materials and their initial grain sizes on the formation of gases （H2, CH4, C2H6 and C3Hs） during serpentinization was investigated by conducting hydrothermal experiments at 311℃ and 3 kbar on olivine and peridotite with initial grain sizes ranging from 〈30 to 177 μm. Hydrocarbons （CH4, C2H6 and C3H8） were produced from reaction between dissolved CO2 in the starting fluids and HE formed during serpentinization, which were analyzed by Gas Chromatography. It was found that olivine serpentinization produced much less H2 and CH4 compared with those after peridotite alteration, while their C2H6 and C3H8 were identical. For example, for olivine with initial grain sizes of 〈30 μm, the amounts of HE and CH4 were 79.6 mmol/kg and 460 μmol/kg after 27 days, respectively. By contrast, the quantities of H2 and CH4 produced in experiment on peridotite with the same run duration were much larger, 119 mmol/kg and 1300 μmol/kg, respectively. This indicates that spinel and pyroxene in peridotite may increase the amounts of HE and hydrocarbons, possibly due to the catalytic effect of aluminum released by spinel and pyroxene during serpentinization. Moreover, the production of H2 and hydrocarbons is negatively correlated with initial grain sizes of the starting material, with smaller amounts of HE and hydrocarbons for larger initial grain sizes, indicating that the kinetics of serpentinization influences the formation of HE and hydrocarbons, possibly because of the lack of catalytic minerals for the starting material with larger grain sizes. This study suggests that olivine cannot completely represent peridotite during serpentinization, and that H2 and hydrocarbons in hydrothermal fields near the mid-ocean ridge may be produced in a very long period of serpentinization or the presence of catalytic minerals due to large grain sizes of ultramafic rocks.
基金support from the National Natural Science Foundation of China(grant number 52075544)Innovation Funds of Jihua Laboratory(X220971UZ230)+1 种基金Basic and Applied Basic Research Foundation of Guangdong Province(2022A1515110649)Funds from Research Platforms of Guangdong Higher Education Institutes(2022ZDJS038).
文摘Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology.In this study,magnesium silicate hydroxide(MSH)nanotubes with serpentine structures were synthesized.The tribological behavior of AZ91D magnesium alloy rubbed against GCr15 steel was studied under lubricating oil with surface-modified MSH nanotubes as additives.The effects of the concentration,applied load,and reciprocating frequency on the friction and wear of the AZ91D alloy were studied using an SRV-4 sliding wear tester.Results show a decrease of 18.7–68.5%in friction coefficient,and a reduction of 19.4–54.3%in wear volume of magnesium alloy can be achieved by applying the synthetic serpentine additive under different conditions.A suspension containing 0.3 wt.%MSH was most efficient in reducing wear and friction.High frequency and medium load were more conducive to improving the tribological properties of magnesium alloys.A series of beneficial physical and chemical processes occurring at the AZ91D alloy/steel interface can be used to explain friction and wear reduction based on the characterization of the morphology,chemical composition,chemical state,microstructure,and nanomechanical properties of the worn surface.The synthetic MSH,with serpentine structure and nanotube morphology,possesses excellent adsorbability,high chemical activity,and good self-lubrication and catalytic activity.Therefore,physical polishing,tribochemical reactions,and physicalchemical depositions can occur easily on the sliding contacts.A dense tribolayer with a complex composition and composite structure was formed on the worn surface.Its high hardness,good toughness and plasticity,and prominent lubricity resulted in the improvement of friction and wear,making the synthetic MSH a promising efficient oil additive for magnesium alloys under boundary and mixed lubrication.
基金supported by the National Natural Science Foundation of China(No.12102356)。
文摘The resource-intensive,high-fidelity infrared signature simulations and Radar CrossSection(RCS)calculations limit the integrated optimization of Unmanned Combat Aerial Vehicles(UCAVs)in response to escalating threats from joint detection systems.To this end,we present a sample-efficient framework to advance the optimization efficiency of UCAV's exhaust system,focusing on both the stealth characteristics evaluation and the optimization process.A novel multi-fidelity stealth assessment method,powered by multi-fidelity neural network and local perceptive fields,has been developed to fuse different fidelity information from infrared radiation signature and RCS values,respectively.Results demonstrate that the method can achieve relatively high accuracy based on a small set of high-fidelity data.Furthermore,this data fusion method is integrated into a multi-objective Bayesian optimization framework.Employing a Gaussian process regression model and the EHVI acquisition function,the framework effectively explores the stealth objective space,achieving a 15.21%hypervolume indicator increase with fewer optimization iterations compared to NSGA-Ⅱ.Results show that the optimized nozzle significantly reduces both the infrared signature and RCS compared to the baseline configuration.The proposed framework offers a practical and efficient approach for optimizing the integrated stealth performance of UCAVs.
基金supported by the National Natural Science Foundation of China(No.22072183)the Natural Science Foundation of Hunan Province,China(No.2022JJ30690)the High Performance Computing Center of Central South University.
文摘Serpentine structured Co_(3)Si_(2)O_(5)(OH)_(4) is inexpensive,chemically stable,and electrochemically active in oxygen evolution reactions(OER).However,the OER activity of Co_(3)Si_(2)O_(5)(OH)_(4) materials is still unfavorable due to the low active sites.Here,Mn^(2+)-doped Co_(3)Si_(2)O_(5)(OH)_(4) serpentine nanosheets with tuned d-band centers are achieved for efficient oxygen evolution in alkaline and neutral electrolytes.The Co_(x)Mn_(3−x)Si_(2)O_(5)(OH)_(4) serpentine nanosheets are synthesized by a simple hydrothermal method.The optimized Co_(2.4)Mn_(0.6)Si_(2)O_(5)(OH)_(4) serpentine nanosheets showed favorable OER overpotentials as well as stable durability in KOH solution and phosphate buffer solution,which were superior to most of the Co-based and Mn-based OER electrocatalysts.The in situ Raman spectroscopy shows that the materials are kept well in the electrochemical OER environments.Further density functional theory shows that the d-band center of Co_(x)Mn_(3−x)Si_(2)O_(5)(OH)_(4) serpentine nanosheets is shifted more upward in comparison with pristine Co_(3)Si_(2)O_(5)(OH)_(4).The changes in the d-band center increase the adsorption of intermediates,optimize the reaction steps,and lower the energy barriers of the OER.That is the main reason for the OER enhancement Mn^(2+)-doped Co_(3)Si_(2)O_(5)(OH)_(4).This work gives an efficient strategy to design cheap and stable electrocatalytic materials for OER in a broad pH environment.
基金supported by the National Science and Technology Major Project of China(No.J2019-Ⅲ-0009-0053)。
文摘The serpentine convergent-divergent nozzle represents an optimal configuration for nextgeneration fighter aircraft characterized by low detectability and high thrust-to-weight ratio.In contrast to the serpentine convergent nozzle,such configuration offers increased design flexibility with additional parameters,leading to heightened interactions among these parameters.As such,it is crucial to reveal the influence of design parameters on the aerodynamic performance of the serpentine convergent-divergent nozzle and the multifactor interaction,as well as its mechanism.Therefore,the influence,interaction and sensitivity of parameters on the aerodynamic performance of the nozzle were numerically investigated using the orthogonal test method.Additionally,the influence mechanism of the convergence angle,throat aspect ratio,and axial length to inlet diameter on the flow characteristics of the nozzle was investigated in detail.The results show that the convergence angle is identified as the main factor affecting the aerodynamic parameters of the nozzle.As the convergence angle increases,the thrust coefficient,total pressure recovery coefficient and discharge coefficient gradually decrease.The interaction between throat aspect ratio and other parameters is obvious.Different design parameters affect the local loss and the friction loss by affecting the curvature and wetted perimeter area,resulting in different aerodynamic characteristics of serpentine convergent-divergent nozzle.
基金the funding received from the Science and Engineering Research Board (SERB), Govt. of India under GAP 3291funded by Ministry of Earth Science (MoES) with project reference number Mo ES/ P.O. (Seismic) 8 (09)-Geochron/2012。
文摘Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydrous uvarovite garnet having Cr_(2)O_(3) upto 19.66 wt% and CaO of 32.12–35.14 wt% in the serpentinized mantle peridotites of Naga Hills Ophiolite(NHO), India. They occur in association with low-Cr diopsides. They are enriched in LILE(Ba, Sr), LREEs, with fractionating LREE-MREE [avg.(La/Sm)_(N) = 2.16] with flat MREE/HREE patterns [avg.(Sm/Yb)_(N) = 0.95]. Raman spectra indicate the presence of hydroxyl(OH^(–)) peaks from 3500 to 3700 cm^(-1). Relative abundances in fluid mobile elements and their close association with clinopyroxenes are suggestive of the formation of uvarovite garnets through low temperature metasomatic alteration of low-Cr diopsides by hydrothermal slab fluids. The high LREE concentration and absence of Eu anomaly in the garnet further attest to alkaline nature of the transporting slab dehydrated fluid rather the involvement of low-p H solution. The chemical characteristics of the hydroxyl bearing uvarovite hosted by the mantle peridotite of NHO deviate from the classical features of uvarovite garnet, and their origin is attributed to the fluid-induced metasomatism of the sub arc mantle wedge in a suprasubduction zone regime.
基金The National Natural Science Foundation of China(No.52071076)Opening Project of State Key Laboratory of Advanced Technology for Float Glass(Grant 2022KF03)are gratefully acknowledged.
文摘The produced water from the oilfield was purified with filter material and then injected back into the ground.The serpentine filter material was easy to harden with the increase in filtration amount,which affected the water quality.A superhydrophilic/underwater oleophobic serpentine filter material was successfully prepared by a simple method of coating modification,which exhibited long-lasting filtration of oily water,good filtration and anti-fouling properties,and resistance to harden.The film-forming material of the superhydrophilic/underwater oleophobic coating was composed of SiO_(2) particles with small size,which could completely and evenly cover the filter particle.The weight loss was only 7.6%after mechanical stirring for 90 min.Compared with the original filter material,the superhydrophilic/underwater oleophobic serpentine filter material showed a better anti-fouling ability and resistance to harden.The filtration of crude oil emulsion and oil slick sewage showed a better backwashing performance.After 35 cycles of continuous filtration of suspended solids in wastewater,the backwashing rate reached 78.4%.The results provided an effective method for the filtration of oily wastewater in the oilfield.
基金supported by the Science Center for Gas Turbine Project,China(Nos.P2022-B-Ⅱ-010-001 and P2022-B-I-002-001)the National Natural Science Foundation of China(Nos.52376032 and 52076180)+2 种基金the Funds for Distinguished Young Scholars of Shaanxi Province,China(No.2021JC-10)the National Science and Technology Major Project,China(No.J2019-Ⅱ-0015-0036)the Fundamental Research Funds for the Central Universities,China(No.501XTCX2023146001).
文摘The high-efficiency Shock Vectoring Control Serpentine Nozzle(SVCSN)takes into account both thrust vectoring and infrared stealth,and significantly improves the comprehensive performance of the aero-engines through an additional auxiliary duct.In this paper,the schlieren photographs at the exit of the high-efficiency SVCSN and the wall static pressure distributions were obtained by experiments,and the numerical results were used to enrich the thrust vectoring characteristics.The effects of the auxiliary injection were analyzed first to reveal the advantages of the high-efficiency SVCSN compared to the conventional SVCSN.Then,the aerodynamic parameters and the structural parameters of the high-efficiency SVCSN were investigated,including the Nozzle Pressure Ratio(NPR),the Secondary flow Pressure Ratio(SPR),the secondary flow relative area and the secondary flow injection angle.Finally,the coupling performance of the high-efficiency SVCSN is studied by using the approximate modeling technology.Results show that the auxiliary injection increases the range between the two shock legs of the “k”shock wave induced by the secondary flow,then causes the separation zone and high-pressure boss of the down wall to expand upstream,and finally results in a prominent increase in the thrust vectoring performance.The thrust vectoring angle and Vectoring Efficiency(VE)of the high-efficiency SVCSN are about 61.6%and 75.7%,respectively,higher than those of the conventional SVCSN at NPR=6.The effects of the NPR and the SPR on the thrust vectoring performance of the high-efficiency SVCSN are coupled with each other.A larger NPR matched with a smaller SPR shows better thrust vectoring performance.The maximum fluctuations in thrust vectoring angle and VE caused by the NPR and SPR are about 22%and 64%.The VE decreases monotonously with the increase of the secondary flow relative area.Smaller secondary flow injection angle shows better thrust vector performance,and the thrust vectoring angle and VE of the secondary flow injection angle of 90are about 20%higher than those of the secondary flow injection angle of 110at NPR=6.Therefore,the secondary flow relative area of 0.06 and the secondary flow injection angle of 90are recommended.
基金Project(2007CB613602)supported by the National Basic Research Program of China
文摘The effect of sodium hexametaphosphate（SHMP） on the separation of serpentine from pyrite and its mechanism were studied systematically through flotation tests,sedimentation tests,surface dissolution,ζ potential tests,adsorption measurements,and infrared spectroscopic analyses.The results show that the SHMP could significantly reduce the adverse effect of serpentine on the flotation of pyrite and make the mixed sample of pyrite and serpentine more disperse in the alkaline condition,thus improve the adsorption of xanthate on pyrite.The action mechanism of the SHMP is that it lowers the pH value at the isoelectric point of serpentine and enhances the negative charge through the dissolution of magnesium from the surface of serpentine and adsorbing on the surface of serpentine.It changes the total interaction energy between serpentine and pyrite from gravitational potential energy to repulse potential energy,according to the calculation of the EDLVO theory.
基金Project(51174229) supported by the National Natural Science Foundation of China
文摘The electrokinetic behavior and surface dissolution of serpentine mineral were studied through Zeta potential measurements, dissolution experiments and X-ray photoelectron spectroscopy. The results show that serpentine has an iso-electric point （IEP） of 11.9, which is higher than that of other phyllosilicate minerals. Dissolution experiments show that the hydroxyl is easy to dissolve with respect to the magnesium cations in the magnesium oxide octahedral sheet. As a result of hydroxyl dissolution, the magnesium ions are left on serpentine surface, which is responsible for serpentine surface charge. The removal of magnesium ions from serpentine surface by acid leaching results in a decrease of serpentine IEP. Therefore, it has been clearly established that the surface charge developed at the serpentine/aqueous electrical interface is a function of the serpentine surface incongruent dissolution.
基金Project(2006AA03Z115) supported by the National High-tech Research and Development Program of ChinaProject(2011CB606302-1) supported by the National Basic Research Program of ChinaProject(50774007) supported by the National Natural Science Foundation of China
文摘An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process （SCRC）,was explored.The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions.The experimental results show that the as-cast ultimate tensile strength can reach about 250MPa and the elongation is 8.6%？13.2%.The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment.Under these experimental conditions,the semi-solid A356 Al alloy slurry with primary α1（Al） grains,which have the shape factor of 0.78？0.89 and the grain diameter of 35？45μm,can be prepared by the serpentine channel pouring process.The primary α2（Al） grains are very fine during the secondary solidification stage.Compared with the conventional HPDC process,the SCRC process can improve the microstructures and mechanical properties of the tensile test samples.The advantages of the SCRC process include easily incorporating with an existing HPDC machine,cancelling the preservation and transportation process of the semi-solid alloy slurry,and a higher cost performance.
基金Project (2011CB606302-1) supported by the National Basic Research Program of China
文摘The semi-solid slurry of 7075 aluminum alloy was prepared by a serpentine pouring channel （SCP）. Influences of pouring temperature and the number of turns on the microstructure of semi-solid 7075 alloy slurry were investigated. The results demonstrated that the semi-solid 7075 aluminum alloy slurry with satisfied quality could be generated by a serpentine pouring channel when the pouring temperature was in the range of 680-700 ℃. At a given pouring temperature, the equivalent size of the primaryα（Al） grains decreased and the shape factor increased with the increase of the number of turns. During the slurry preparation of semi-solid 7075 aluminum alloy, the flow direction of alloy melt changed many times when it flowed in a curved and closed serpentine channel. With the effect of“stirring”in it , the primary nuclei gradually evolved into spherical and near-spherical grains.
基金Project (50774007) supported by the National Natural Science Foundation of ChinaProject (20082022) supported by the Scientific Research Foundation for Doctors from Taiyuan University of Science and Technology, China
文摘The integral microstructure of semisolid A356 alloy slurry with larger capacity cast by serpentine channel was studied and the influence of cooling ability of serpentine channel on the microstructure was investigated. The results indicate that ideal slurry with larger capacity can be prepared through serpentine channel with good cooling ability. When the serpentine channel was continuously cooled, both the longitudinal and the radial microstructure of the slurry was composed of granular primary phase and the integral microstructure uniformity of the slurry was good. However, uncooled serpentine channel can only produce larger slurry with fine grains in positions adjacent to its centre and with a large number of dendrites in positions close to its edge, thus, the radial microstructure of larger slurry is nonuniform. The pouring temperature is set up to 680 °C and the solid shell inside the channel can be avoided at this pouring temperature.
基金Project(51574061)supported by the National Natural Science Foundation of ChinaProject(N150106004)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2014SKY-WK011)supported by the Open Fund Project of Shaanxi Key Laboratory of Comprehensive Utilization of Tailings Resources,China
文摘The magnetism of pentlandite surface was enhanced through the selective precipitation of micro-fine magnetite fractions on pentlandite surfaces. This was achieved through adjustment of slurry pH and addition of surfactants. The results showed that at pH 8.8 with the addition of 100 g/t sodium hexametaphosphate, 4.5 L/t oleic acid, and 4.5 L/t kerosene, significant amount of fine magnetite particles adhered to the pentlandite surface, while trace amount of coating was found on serpentine surfaces. Thus, the magnetism of pentlandite was enhanced and pentlandite was well separated from serpentine by magnetic separation under the magnetic field intensity of 200 kA/m. Scanning electron microscopy （SEM） and zeta potential measurement were performed to characterize changes of mineral surface properties. Calculations of the extended Derjaguin-Landau-Verwey-Ocerbeek （EDLVO） theory indicated that, in the presence of surfactants the total interaction energy between magnetite and pentlandite became stronger than that between magnetite and serpentine. This enabled the selective adhesion of magnetite particles to pentlandite surfaces, thereby enhancing its magnetism.
基金Project(2011CB606300)supported by the National Basic Research Program of ChinaProject(5077400)supported by the National Natural Science Foundation of China
文摘The semi-solid slurry of A380 aluminum alloy was prepared by the serpentine channel. The effects of pouring temperature, curve number and curve diameter of the serpentine channel on the microstructure of the semi-solid A380 aluminum alloy slurry were investigated. The results show that the satisfactory semi-solid A380 aluminum alloy slurry could be obtained when the pouring temperature ranged from 630 to 650 °C. Under the same conditions, increasing the curve number or reducing the curve diameter of the serpentine channel would decrease the average diameter and increase the shape factor of the primary α（Al） grains. The ＂self-stirring＂ of the alloy melt in the serpentine channel was beneficial to the ripening of the dendrites and the spheroidizing of the primary α（Al） grains.
基金Project (2006AA03Z115) supported by the National High-tech Research and Development Program of ChinaProject (2006CB605203) supported by the National Basic Research Program of ChinaProject (50774007) supported by the National Natural Science Foundation of China
文摘Semi-solid A356 aluminum alloy slurry was prepared by using serpentine channel pouring process, and the influences of the channel diameters and pouring temperatures on the semi-solid A356 aluminum alloy slurry were investigated. The experimental results show that when the channel diameter is 20 and 25 mm, respectively, and the pouring temperature is 640-680 ℃, the average diameter of primary α（Al） grains in the prepared A356 aluminum alloy slurry is 50-75 and 55-78 μm, respectively, and the average shape factor of primary α（Al） grains is 0.89-0.76 and 0.86-0.72, respectively. With the decline in the pouring temperature, the microstructure of semi-solid A356 aluminum alloy slurry is more desirable and a serpentine channel with smaller diameter is also advantageous to the microstructure imProvement. During the preparation of semi-solid A356 aluminum alloy slurry, a large number of nuclei can be produced by the chilling effect of the serpentine channel, and owing to the combined effect of the chilled nuclei separation and melt self-stirring, primary α（Al） nuclei can be multiplied and spheroidized finally.
