AZ91D镁合金低压交流氧化成膜机制

基于一种低的交流电压条件(10 V),在NaOH和Na₂SiO₃的混合溶液体系中,对AZ91D镁合金进行电化学阳极氧化处理.利用扫描电镜(SEM)、X射线能谱仪(EDS)、X射线衍射仪(XRD)、电化学测试技术等手段研究了AZ91D镁合金表面阳极氧化的成膜过程、膜层生长的特点以及氧化工艺参数对膜层性能的影响规律.试验结果表明:在10 V这样低的交流电压下,在镁合金表面获得的氧化膜层表面均匀,为无孔洞的平层状膜层,其生长过程呈叠加式特点;获得的氧化膜层的主要成分为Mg₂SiO₄;在质量分数为3.5%的NaCl溶液中,经过电化学阳极氧化的镁合金的耐蚀性优于未经处理的镁合金.      

硅溶胶在镁合金阳极氧化反应中的成膜作用

采用溶胶化学与电化学相结合的新型表面处理方法——将自制的硅溶胶添加到电解质溶液中进行阳极氧化.以AZ91D镁合金及镁锂合金为研究基材,研究体系分别为硅酸钠和氢氧化钠溶液,通过对不同溶胶添加量下的溶液电导率、反应击穿电压、氧化膜层厚度及微观形貌、膜层表面成分及XRD结果分析,来探讨溶胶粒子在成膜过程中的作用.结果表明:溶胶粒子的加入增大了阳极表面的电阻,使得反应的击穿电压升高,从而导致了膜层厚度增加;同时硅溶胶粒子参与了阳极氧化反应,其在高温高压的条件下与MgO生成了Mg₂SiO₄.      

氯离子和温度对铝合金在冷却液中腐蚀的影响

分别采用了动电位极化法、电化学阻抗法研究了不同温度下、不同氯离子浓度下防锈铝在模拟冷却液中的腐蚀行为,采用金相显微镜和扫描电镜对极化后防锈铝的表面特征进行了观察和记录。结果表明,氯离子吸附在防锈铝氧化膜表面,对氧化膜表面造成破坏。在一定温度下（30℃）,当氯离子浓度超过0.01mol/L时,中间产物吸附作用就会增强,阻抗谱中低频区出现感抗弧,点蚀萌生。随着氯离子浓度增高（超过0.01mol/L）,防锈铝的腐蚀加剧,耐腐蚀性能下降。随着温度的升高,阴极和阳极反应阻力变小,阳极金属铝的溶解和阴极氧还原速度增大,腐蚀速度增大。温度升高的同时,溶解氧含量下降,阴极反应受到抑制。与此同时扩散过程在整个腐蚀反应过程中的支配性降低,中间产物在氧化膜表面的吸附作用增强,从而导致低频容抗弧的出现。温度对点蚀形貌的影响主要体现在影响单个点蚀坑的几何大小,促进点蚀坑的生长。      

贫燃型汽车尾气NOx的催化净化

用溶胶-凝胶混合法制备了Al₂O₃,Ag/Al₂O₃,Sn/Al₂O₃,Ga/Al₂O₃,Co/Al₂O₃和Pt/Al₂O₃等催化剂.在相同实验条件下,比较了C₃H₆在这些催化剂上还原NO的活性,并考察了反应条件对C₃H₆和CH₃OH在Ag/Al₂O₃上还原NO性能的影响.结果表明,Ag/Al₂O₃的还原NO活性优于其它催化剂.H₂O对Ag/Al₂O₃催化剂的NO还原具有可逆抑制作用,SO₂降低C₃H₆在Ag/Al₂O₃上还原NO的活性,但会显著提高CH₃OH还原NO的活性.     

2198铝合金硫酸-己二酸阳极氧化膜耐蚀性

以2198铝-锂合金为研究对象,在硫酸-己二酸电解质溶液中进行阳极氧化,并对氧化后的试样进行沸水封闭处理。采用场发射扫描电子显微镜(FE-SEM)和原子力显微镜(AFM)对氧化膜的表面和截面的形貌进行观察。通过电化学阻抗谱(EIS)、塔菲尔(Tafel)曲线和浸泡实验来分析阳极氧化膜的耐蚀性能。结果表明铝-锂合金在阳极氧化过程中由于含铜合金相的影响,形成的氧化膜孔洞不完整出现连通现象;电化学测试结果表明封闭之后的氧化膜的耐蚀性明显提高,并且随着浸泡时间的延长拟合等效电路发生改变,同时多孔层和阻挡层的阻抗值在降低,说明在浸泡的过程中氧化膜的结构发生改变,耐蚀性降低。      

LY12cz铝合金晶间腐蚀模拟试验研究

用金属间化合物 θ(CuAl₂)、S(Al₂CuMg)、MnAl₆与纯Al(L1)组成多电极体系,以模拟LY12cz合金的晶界区.通过电化学测试、SEM和能谱分析等方法研究了该合金晶间腐蚀机理.证实其晶间腐蚀是由沿晶界偏析的强化相与贫Cu区所组成的多电极体系引起的.在含Cl^－离子的中性溶液中,S相是导致晶间腐蚀的主要阳极相.S相首先发生阳极溶解,随后,贫铜区、MnAl₆相逐步随S相一起溶解.以这种方式沿晶界形成了阳极溶解通道,导致晶间腐蚀.     

低电压(10V)下镁合金表面电化学氧化膜层

基于高电压下氧化成膜有可能对镁合金基材机械性能造成损伤.研究了在以硅酸钠为主要成分的电解液中,施加10~110V交流电压对AZ91D镁合金表面进行电化学氧化的成膜过程.探讨了氧化电压、氧化时间等对膜层性能的影响规律,并且对所获得氧化膜层进行了微观分析.结果表明:在10V电压下氧化就能获得与70~110V电压下耐腐蚀性相当的氧化膜层;而且在10V交流电压下获得的氧化膜层形成过程为颗粒状形式-连接成块状-完整的膜层-交错叠式生长等4个阶段.     

Occurrence features of simultaneous H+- and He+-band EMIC emissions in the outer radiation belt

As an important loss mechanism of radiation belt electrons, electromagnetic ion cyclotron (EMIC) waves show up as three distinct frequency bands below the hydrogen (H⁺), helium (He⁺), and oxygen (O⁺) ion gyrofrequencies. Compared to O⁺-band EMIC waves, H⁺- and He⁺-band emissions generally occur more frequently and result in more efficient scattering removal of <～5?MeV relativistic electrons. Therefore, knowledge about the occurrence of these two bands is important for understanding the evolution of the relativistic electron population. To evaluate the occurrence pattern and wave properties of H⁺- and He⁺-band EMIC waves when they occur concurrently, we investigate 64 events of multi-band EMIC emissions identified from high quality Van Allen Probes wave data. Our quantitative results demonstrate a strong occurrence dependence of the multi-band EMIC emissions on magnetic local time (MLT) and L-shell to mainly concentrate on the dayside region of L?=?～4–6. We also find that the average magnetic field amplitude of H⁺-band waves is larger than that of He⁺-band waves only when L?<?4.5 and AE¹?<?300?nT, and He⁺-band emissions are more intense under all other conditions. In contrast to 5 events that have average H⁺-band amplitude over 2 nT, 19 events exhibit >2 nT He⁺-band amplitude, indicating that the He⁺-band waves can be more easily amplified than the H⁺-band waves under the same circumstances. For simultaneous occurrences of the two EMIC wave bands, their frequencies vary with L-shell and geomagnetic activity: the peak wave frequency of H⁺-band emissions varies between 0.25 and 0.8 f_cp with the average between 0.25 and 0.6 f_cp, while that of He⁺-band emissions varies between 0.03 and 0.23 f_cp with the average between 0.05 and 0.15 f_cp. These newly observed occurrence features of simultaneous H⁺- and He⁺-band EMIC emissions provide improved information to quantify the overall contribution of multi-band EMIC waves to the loss processes of radiation belt electrons.     

Quantifying lunar soil composition with partial least squares modeling of reflectance

Retrieval of lunar soil composition is commonly achieved through optical remote sensing in which spectral characteristics of returned lunar samples are related to their constituents. Partial least squares (PLS) and principal component regression (PCR) were applied to the dataset characterized by the Lunar Soil Characterization Consortium (LSCC) to estimate the content of FeO, Al₂O₃ and TiO₂ in the soils. The goal of this study was to test whether the conversion of reflectance to single scattering albedo (SSA) via Hapke’s radiative transfer model is able to improve the performance of PLS and PCR. Results from PLS and PCR modeling of SSA spectra indicate that the conversion does not necessarily improve the performance of PLS and PCR, and this depends on the chemical considered, the way to select the number of optimal factors, and how the data were pretreated. The conversion failed to accommodate the large deviation of highland samples with low FeO, TiO₂ and high Al₂O₃.     

Rocket-borne measurements of atmospheric infrared emissions by spectrometric techniques

As part of the MAP/WINE Campaign 1983/84 a liquid helium cooled infrared grating spectrometer measured night zenith radiances of CO₂, O₃, and H₂O in the mesosphere and lower thermosphere. From a comparison of the measured spectral radiances with results from LTE radiative transfer calculations atmospheric temperatures and concentration profiles of H₂O and O₃ were determined, showing some interesting features. The ozone densities obtained appear to contradict model predictions based upon the assumption that ozone is in photochemical equilibrium at mesospheric heights. Since the ozone density distribution shows quite similar structures as the vertical wind profile, transport effects seem to play a major role in the mesospheric ozone formation.     

Plasma chemical reactions in C2H2/N2, C2H4/N2, and C2H6/N2 gas mixtures of a laboratory dielectric barrier discharge

Plasma chemical reactions in C₂H₂/N₂, C₂H₄/N₂, and C₂H₆/N₂ gas mixtures have been studied by means of mass spectrometry at a medium pressure of 300 mbar in a laboratory dielectric barrier discharge. A major reaction scheme is production of larger hydrocarbons like C_nH_m with n up to 12 including formation of functional CN groups.     

Mesospheric H2O and H2O2 densities inferred from in situ positive ion composition measurement

The measurements of positive ion composition in the high latitude D-region have revealed an excess of 34⁺ under distrubed conditions which has been interpreted as H₂O₂⁺. At the same altitude range near the transition height oxonium ions were measured as well. This paper presents a new model for the production and loss of oxonium ions with their production from H₂O₂⁺ + H₂O → H₃O⁺ + HO₂ and their loss by attachment of N₂ and/or CO₂. A reaction constant of 8.5×10^?28 (300/T)⁴ cm⁶s^?1 has been obtained for the three body attachment H₃O⁺ + CO₂ + M → H₃O⁺.CO₂ + M from the measured density profile of 63⁺ in flight 18.1020. Mesospheric H₂O and H₂O₂ densities are inferred from measurements of four high latitude ion compositions based on the oxonium model. The mixing ratios of hydrogen peroxide are up to two orders of magnitude higher compared to previous model calculations. In order to explain the missing production of odd hydrogen, we consider larger O(¹D) densities, surface reactions of O(³P) on particles, and cathalytic photodissociation of water vapor on aerosol particles.     

Quantitative determination of the outgassing water vapor concentrations surrounding space vehicles from ion mass spectrometer measurements

Outgassing from materials as well as deliberate gaseous and liquid releases create contaminant clouds around spacecraft that can degrade both instrumentation and measurements. This paper describes a new method for estimating outgassing water vapor concentrations around space vehicles. Water vapor ions measured in the course of a rocket experiment performed at Eglin AFB, Florida, on December 12, 1980 at 2311 UT are utilized to demonstrate the technique. The H₂O concentration near the payload's surface is calculated using the rate coefficient for the fast charge transfer process, O⁺ + H₂O + H₂O⁺ + O, the source of the observed water vapor ions. It is found that the measured H₂O⁺ ions were produced within 3–4 cm of the sampling plate's surface and that the average H₂O pressure over this distance was relatively constant on ascent at 8 × 10^?6 torr, within a factor two, implying a steady outgassing rate.     

一种单喷嘴推力室燃烧内流场的方法

为了方便开展单喷嘴气气喷注器燃烧试验研究,设计了一种燃烧室壁面测温,并结合推力室燃烧流场的非稳态数值模拟的方法,以考察燃烧室内流场的发展和燃烧完成情况.应用试验数据对不同的湍流模型和燃烧模型进行了对比研究,得到与试验结果较为吻合的计算模型.并应用该方法开展了同轴剪切式喷注器氢/氧喷注动量比、燃烧室压力变化的试验研究.试验结果表明喷注器掺混燃烧效果随氢/氧喷注动量比增加而增强,而不随燃烧室压力的变化而变化.     

Radiative cooling in the NLTE region of the mesosphere and lower thermosphere—Global energy balance

Radiative cooling in the mesosphere and lower thermosphere is predominantly from 15-μm emissions of CO₂. Above t 120 km, complete NLTE cooling from NO becomes more important. Above 100 km, both the CO₂ and the NO cooling are proportional to concentrations of atomic oxygen which are dynamically controlled and poorly characterized by observations. Furthermore, the rate for energy exchange between O and CO₂(ν₂ = 1) is very poorly known. CO₂ is close to LTE throughout the mesosphere, but small departures from LTE between 65 and 80 km may be important for questions of remote sensing. Remote sensing for trace gases, e.g., O₃ and H₂O, must consider NLTE effects in the mesosphere. A global mean column model for aeronomy processes above 65 km gives a reasonable agreement with observed temperatures, suggesting that radiative balance may be possible without the need for including eddy cooling or gravity wave heating.     

The variability of stratospheric nitrogen compounds observed by LIMS in the winter of 1978–1979

The LIMS experiment was launched on the Nimbus 7 satellite for the purpose of sounding the vertical structure of temperature and key upper atmosphere trace gases on a global scale. The technique of thermal infrared limb sounding was used to obtain measurements of O₃, H₂O, NO₂, and HNO₃. LIMS collected data almost continuously from late October to late May over the latitude range from 64°S to 84°N. Two of the gases, NO₂ and HNO₃, are important elements in the NO_x chain of chemical reactions leading to ozone destruction. We will describe results for these gases in terms of zonal mean profiles and latitudinal distributions. The period selected for study is January–May 1979, when a major stratospheric warming occurred.     

Study on O2 generation and CO2 absorption capability of four co-cultured salad plants in an enclosed system

The ability to generate O₂ and absorb CO₂ of several co-cultured vegetable plants in an enclosed system was studied to provide theoretical reference for the future man-plant integrated tests. Four kinds of salad plants (Lactuca sativa L. var. Dasusheng, Lactuca sativa L. var. Youmaicai, Gynura bicolor and Cichorium endivia L.) were grown in the CELSS Integration Test Platform (CITP). The environmental factors including O₂ and CO₂ concentration were continuously monitored on-line and the plant biomass was measured at the end of the test. The changing rules of O₂ and CO₂ concentration in the system were basically understood and it was found that the O₂ generated by the plants could satisfy the respiratory needs of 1.75 persons by calculation. It was also found that the plants could absorb the CO₂ breathed out by 2 persons when the light intensity was raised to 550 mmol m⁻² s⁻¹ PPF. The results showed that the co-cultured plants hold good compatibility and excellent O₂-generating and CO₂-absorbing capability. They could also supply some fresh edible vegetable for a 2-person crew.