液氮罐内低温氮气的温度场研究

对装有少量液氮的液氮罐内的温度分布进行了系统研究,提出了相应的温度分布模型.研究表明,在10 L容积的液氮罐内注入少量液氮时,罐内温度可保持低于-130℃持续约25天,适用于多种场合的超低温保存.通过调节距离液氮面的高度,可选择保存样品的温度范围并控制样品的升降温速度.理论计算的温度分布与测量的结果符合较好,证实了所建立模型的合理性和有效性.     

Corrosion failure of 1Kh18N9T [1Cr18Ni9Ti] steel in liquid lithium

This article describes corrosion and mechanical tests on 1Kh18N9T[lCrl8Ni9Ti] steel specimens previously held in molten lithium (of various degrees of purity) at 700, 800, and 900° C both under isothermal conditions and in the presence of concentration- and heat-induced mass transfer. The results of gravimetric, spectrographic, and metallographic analyses showed that the corrosive action of lithium on the steel studied takes the form of dissolution of steel constituents and intergranular penetration of the steel by molten lithium. The role of nitrogen and oxygen in the corrosion process was estimated and it was established that even weak currents of liquid lithium intensify its corrosive action on 1Kh18N9T steel.     

Suppression of Type IV fracture in welded joints of advanced ferritic power plant steels – effect of boron and nitrogen

Abstract

The effect of boron and nitrogen on the grain refinement in HAZ during heating and on the Type IV fracture in welded joints has been investigated for P92 and 9Cr–3W–3Co–VNb steel containing boron and or nitrogen. Creep tests were carried out at 650°C (923 K) for up to about 3 × 10⁴ h for base metals, simulated HAZ specimens and welded joints. The addition of boron of 47 to 139 ppm to 9Cr – 3W–3Co–VNb steel containing minimized nitrogen as low as 10–20 ppm suppresses the grain refinement in HAZ and hence suppresses the Type IV fracture in welded joints at low stresses. The addition of excess nitrogen of 0.06% causes the grain refinement during heating at around Ac3 temperature, in both conditions of no boron and high boron of 130 ppm. A combination of high boron of 130 ppm and low nitrogen of 80 ppm causes no grain refinement in HAZ during heating at around Ac3 temperature as well as significant improvement of creep rupture strength of base metal by fine MX nitrides without any formation of boron nitrides.     

Production of high nitrogen surfaces on 2205 duplex stainless steel substrate using the PTA technique

Abstract

The plasma transferred arc technique has been used for the production of high nitrogen surfaces on 2205 duplex stainless steel substrates. Nitrogen was introduced into the melt using Ar+5%N₂ and Ar+10%N₂ gas mixtures. The nitrided surfaces are austenitic–ferritic and have a thickness of 1140±35 and 1650±31 μm respectively. The change of the austenite crystal lattice, due to the absorption of nitrogen, was determined by X-ray diffraction. Pin on disc tests showed that the wear resistance was increased. The corrosion in 3·5%NaCl and 1 N H₂SO₄ aqueous solutions was also slightly improved. Significant improvement was, however, observed in the pitting corrosion resistance of the nitrided surfaces, with regard to the 2205 duplex stainless steel substrate.     

碳氮含量对含钒铁素体不锈钢高温性能的影响

为研究碳氮含量对其高温热拉伸及热压缩性能的影响,以含钒铁素体不锈钢为实验材料,采用Gleeble3500试验机进行热模拟实验,并对热压缩后试样的显微组织进行了金相观察和SEM检测,对析出相采用TEM分析.结果表明:钒元素的加入在一定程度上提高了材料的高温性能;在实验设计的成分范围内,较高的氮含量和低的碳含量组合能在保证材料韧塑性的前提下提高强度;热压后缓冷至室温,材料中将出现部分马氏体组织.     

氮流量对TaN薄膜微结构及性能的影响

采用反应直流磁控溅射法在Al2O3陶瓷基片上制备TaN薄膜,研究了氮流量(N2/(N2+Ar))对TaN薄膜微结构及性能的影响。结果表明,随氮流量的增大,TaN薄膜的氮含量、电阻率、方阻以及TCR的绝对值逐渐增大,而沉积速率逐渐降低。当N2流量较低(2%～4%)时,TaN薄膜中主要含有电阻率和TCR绝对值较低的六方Ta2N相(hcp),薄膜的电阻率在344μΩ.cm到412μΩ.cm范围内,薄膜的TCR绝对值约为几十ppm/℃。当氮气流量较高(5%～6%)时,薄膜中Ta2N相消失,薄膜中主要含有TCR绝对值较大的体心四方结构(bct)的TaN和四方结构(bct)的Ta3N5相,薄膜的电阻率在940μΩ.cm到1030μΩ.cm范围内,薄膜的TCR绝对值约为几百ppm/℃。     

Correlation between texture,earing behaviour and dissolved carbon and nitrogen

The present study compared the differences of texture and earing behaviour in DR tinplate steel sheets. Dissolved carbon and nitrogen contents were discussed as the principal factor. The {001}?110? texture component whose earing tendency is higher than that of heterogeneous {111} fibre texture, is harmful for earing property and needed to be reduced to minimum in most cases. The increase of the dissolved carbon and nitrogen contents is responsible for weaker {111} fibre texture and more intense {001}?110? component. Additionally, a strong {114}?110? texture component was observed on condition of higher dissolved carbon and nitrogen contents and its formation mechanism was discussed.     

Effect of nitrogen on biocorrosion behavior of high nitrogen nickel-free stainless steel in different simulated body fluids

The aim of this research is to study the biocorrosion behavior of high nitrogen nickel-free stainless steel (HNS) with different nitrogen content, also with comparison to AISI 317L, in three different simulated body fluids. The comparison was focused on the influence of nitrogen in HNS and different protein solutions on the passive behavior using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and capacitance measurements (Mott-Schottky approach). The study revealed that HNS possessed thicker and more protective passive films with increase of nitrogen, which could improve the biocorrosion resistance and biocompatibility after implanted. The passive films behaved as n-type semiconductors and showed a decrease in donor density by nitrogen addition, thus indicating more beneficial for haemocompatibility. The electrochemical behavior recorded in the albumin and fibrinogen solutions revealed protein played an important role in the biocorrosion of HNS, which could result in the breakout of passive films and enhance the corrosion rate by means of chelation.     

Effect of nitrogen and vanadium on austenite grain growth kinetics of a low alloy steel

Austenite grain growth kinetics in a steel containing 0.4% C, 1.8% Cr with different nitrogen contents (in the range 0.0038–0.0412%) and a micralloying addition of 0.078% V were investigated. The investigations were carried out in an austenitising temperature range of 840–1200 °C for 30 min. The results of investigations showed that N promotes the grain growth of austenite. The microalloying addition of vanadium protects the austenite grain growth because of carbonitride V(C,N) precipitation and the grain boundary pinning effect of undissolved particles of V(C,N). Using a thermodynamic model, the carbonitride V(C,N) content, undissolved at the austenitising temperature was calculated. At temperatures when a coarsening and dissolution of carbonitride occurs, the austenite grains start to growth. The effect of nitrogen on the type of chord length distribution of austenite grains was analysed.     

Microstructural thermostability of high nitrogen austenitic stainless steel

A high nitrogen austenitic stainless steel, Fe–24Mn–18Cr–3Ni–0.62N, was isothermally annealed from 750 to 900 °C for different times to investigate the thermostability of its microstructures. Results show that the precipitates were Cr₂N and initially formed along the grain boundary. The time–temperature–precipitation diagram was established, according to which the critical cooling rate of this material with less than 0.1–0.5 vol.% of precipitated Cr₂N was specified as 30 °C/min. The microhardness of the matrix in samples annealed at different temperatures decreased with the diffusion of nitrogen from the matrix to grain boundaries.     

膜吸收法应用于氨氮废水净化的研究

在去除废水里氨氮的3种膜吸收方式中,吸收式膜吸收法能在最短时间内将水中氨氮降至较低水平.因此,它被认为是最有效的方法.研究表明,废水的pH是影响传质系数的最主要因素;氨氮浓度对膜通量影响较大,氨氮浓度越高,氨的膜通量越大;废水中氨氮或盐量较高时,能有效抑制水的渗透蒸馏通量,减弱对吸收液的稀释作用.通过运用吸收式膜吸收法对以无机污染物为主的高氨氮废水和以有机污染物为主的剩余氨水处理效果作对比研究,进而得出以下结论:膜吸收法适用于处理含盐量较高、中温、油性污染物含量较低的高氨氮废水.最后还初步探讨了膜的污染和再生情况.     

液氮温度下分子筛的真空吸附特性试验研究

为探究低温容器夹层所用分子筛吸附剂的吸附特性,采用静态膨胀法进行试验,获得了平衡压力为10-3Pa～103Pa范围内4A、5A和13X分子筛对N2、O2单一组分以及空气的吸附等温线,比较了不同分子筛对气体的吸附能力差异,探究了分子筛的吸附机理.研究结果表明:液氮温度下,5A和13X分子筛在真空条件下对N2及O2的吸附性...     

Discontinuous precipitation of Cr2N in a high nitrogen,chromium-manganese austenitic stainless steel

The main purpose of the present work is to study the effect of a high nitrogen content (1 wt% N), on the microstructural evolution of a Cr-Mn austenitic stainless steel aged over the [400–900 °C] temperature interval. Thermal treatments carried out between 700 and 900 °C lead to the decomposition of the nitrogen supersaturated austenitic matrix by discontinuous precipitation of Cr₂N particles. The microstructural features of the reaction are described and analysed. In the present case, the cellular precipitation of Cr₂N is a peculiar and complex phenomenon which involves two diffusion mechanisms: the diffusion of an interstitial element (nitrogen) and the diffusion of a substitutional one (chromium). The nucleation of the discontinuous precipitation arises from a reduction of the surface energy of the precipitates. Furthermore, the precipitation growth is a non-steady state process, because the reaction is governed at first by the intergranular diffusion of chromium, and then tends to be controlled by its bulk diffusion. Consequently, the features of this discontinuous precipitation do not fit in with the assumptions of usual theories, which have been established for binary substitutional systems that transform in steady state conditions. This discontinuous precipitation brings about a slight hardening. Then, the hardness of the aged samples can be described by an additive relationship between the hardness of the precipitation cells and that of the untransformed matrix. Beside the discontinuous precipitation of Cr₂N, sigma phase forms with significant volume fractions.     

基于焊道尺寸控制的电弧增材成形高氮奥氏体不锈钢与316L不锈钢交织结构EI北大核心CSCD

采用高氮奥氏体钢与316L不锈钢丝材,对高氮奥氏体不锈钢熔覆焊道、单道多层、单层多道表面成形特性进行分析,筛选适宜的工艺参数。通过控制两种材料焊道尺寸,获得最适用于成形异材交织结构的工艺参数。利用不同道间距实验得到异材焊道的最佳道间距,并采用合理路径,制备电弧增材成形交织结构。结果表明:工艺参数的变化对高氮奥氏体不锈钢焊道表面成形特性影响极大,易出现气孔;提出异材焊道几何尺寸、截面面积匹配误差法,获得最佳工艺参数:其中高氮奥氏体钢丝材的送丝速率为5.7 m/min,316L不锈钢丝材的送丝速率为5.6 m/min,焊接速率均为0.6 m/min。通过降低起弧次数,采用闭合路径,提高了异材交织结构成形精度,减少了后处理加工。     

Effect of low nitrogen content on work hardening and microstructural evolution in Hadfield steel

Nitrogen content in austenitic manganese steels is usually not reported nor standardized. The present work has found that it typically ranges between 130 ppm and 200 ppm in solution. Microstructural evolution has been studied by optical microscopy, using mainly differential interference contrast mode. Work hardening was analyzed under compression conditions using Hollomon's fitting and Vickers microindentation hardness measurements at different deformation levels. Even low contents of nitrogen in solution exhibit a significant effect on the slope of stress–strain curves, with strain-hardening exponent values of 0.7, 0.57 and 0.41 for 720 ppm, 130 ppm and 71 ppm of nitrogen, respectively. It was also found that the nitrogen content influences the microstructure of deformed coarse grained polycrystalline austenite, leading to twining and shear bands at the upper level of nitrogen, while it was not clearly found in the samples with lower nitrogen content.     

The effect of micro alloying elements (vanadium,titanium) additions on the austenite grain growth behavior in medium carbon steel containing nitrogen

The austenite grain growth behavior of microalloying elements free steel (nitrogen steel) and micro alloyed steel (V−N steel and V−Ti−N steel) was investigated. The equilibrium dissolving behavior of precipitates was calculated by thermodynamic software and the morphology was observed by tunneling electron microscope. Moreover, grain growth kinetics was analyzed through theoretical calculation. Results show that the austenite grain size of V−N steel and V−Ti−N steel are significantly refined by the undissolved precipitates compared to nitrogen steel. Due to higher dissolving temperature of (vanadium, titanium)(carbon, nitrogen), the austenite grain of V−Ti−N steel keeps fine and increases slowly from 900 °C to 1250 °C. The difference of activation energy between V−N steel and V−Ti−N steel was supposed to come from the effect of different kinds of precipitates on the austenite grain growth. Compared to the vanadium rich (vanadium, titanium)(carbon, nitrogen), the titanium rich (vanadium, titanium)(carbon, nitrogen) is larger and more stable in view of its existence at higher temperature. The decrease of pinning forces can be attributed to the decrease of volume fraction and increase of radius of (vanadium, titanium)(carbon, nitrogen). Compared with critical grain sizes, the larger experimental grain sizes lead to grain growth from 900 °C to 1250 °C.     

Precipitation Behavior of TiN in Bearing Steel

The precipitation behavior of titanium nitride (TIN) in bearing steel and effects of TiN inclusions on quality of the steel have been studied by thermodynamic calculation and experiment. The results show that with the increase of the content of Ti and [N], the properties of bearing steel decreased; adjusting the content of N and Ti could influence the precipitation occasion and condition of TiN in the steels. If Ti content is less than 30x10-6 and nitrogen content is less than 53x10-6, the temperature of TiN precipitation is under the solidus temperature and the size "\s small so that they have little harmful and even beneficial effect on the properties owing to grain refinement.     

Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels

The microstructure evolution and intergranular corrosion (IGC) behavior of high nitrogen martensitic stainless steels (MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M₂₃C₆ to M₂N, furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.     

Spectroscopic investigation of methylated amines by a cavity-ringdown-based spectrometer

High-resolution absorption spectra of gas-phase monomethylamine (MMA, CH(3)NH(2)) and dimethylamine [DMA, (CH(3))(2)NH] in the region of the first overtone of the NH stretch vibration are reported. Measurements were performed with a near-infrared laser spectrometer based on the cavity-ringdown (CRD) detection technique. The minimum detectable absorption coefficient for the CRD detection setup is alpha(min)=1.55 x 10(-8) cm(-1) (for SNR = 1). This corresponds to detection limits of 350 parts in 10(9) (ppb) for MMA and 1.6 parts in 10(6) (ppm) for DMA in synthetic gas mixtures under interference-free conditions, or 10 ppm and 60 ppm for MMA and DMA, respectively, in the case of gas mixtures such as exhaled human breath containing H(2)O, CO(2), and other absorbing gases in this range.     

Preparation,characterisation and kinetics of corn-shaped Ag nanoparticles

Conventional UV-vis spectroscopic and transmission electron microscopy methods were used to monitor the kinetics, formation and characterisation of silver nanoparticles in the methionine-promoted reduction of silver(I). The silver nanoparticles (purple colour; λ _max?=?550?nm) are corn-shaped and aggregated, and the average particle size is about 23?nm. The kinetics of silver nanoparticles formation has been studied as a function of [Ag(I)], [methionine] and [CTAB]. We see that [Ag(I)] has no effect on the rate of silver nanoparticles formation. At higher [CTAB]?≥?40.0?×?10^?4?mol?dm^?3, silver nanoparticles were not observed. Methionine is responsible for interparticle interaction, increase in aggregate size and cross-linking between the particles, and it acts as complexing, reducing, adsorbing and capping agents. A mechanism consistent with the observed kinetics has been proposed and discussed.