CO2分压对N80油管钢在CO2驱注井环空环境中应力腐蚀行为的影响

使用恒应变试样浸泡试验、表面分析技术和电化学测试技术研究了CO₂分压对N80钢在模拟CO₂驱注井环空环境中应力腐蚀行为的影响。研究结果表明:CO₂分压对腐蚀速率的影响存在一个拐点,环境温度为25 ℃时拐点约为1 MPa。当CO₂分压小于1 MPa时,由于腐蚀产物膜（FeCO₃）成形较慢,覆盖率低,随CO₂分压的增高,N80钢的自腐蚀电流密度快速增大;当CO₂分压大于1 MPa时,腐蚀产物膜能以较快的速率成形,覆盖率高,CO₂分压的进一步增高反会使得N80钢的腐蚀电流密度降低。CO₂溶于模拟环空溶液中会使溶液pH持续下降,促使N80油管钢在环空环境下发生应力腐蚀开裂。N80钢在CO₂注入井环空环境中的应力腐蚀开裂机制是阳极溶解和氢脆共同作用的混合机制。应力腐蚀裂纹在萌生阶段局部阳极溶解作用（点蚀）为主导,该作用下CO₂分压为1 MPa时应力腐蚀裂纹最易萌生;在应力腐蚀裂纹生长阶段氢脆作用更强,这种作用导致CO₂分压更高时应力腐蚀裂纹更容易生长,应力腐蚀敏感性进一步提高。      

Effects of annealing temperature on structure and electrical properties of sol–gel derived 0.65PMN-0.35PT thin film

0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (0.65PMN-0.35PT) thin films were deposited on Pt/Ti/SiO₂/Si substrates annealed from 550 to 700 °C using sol-gel process. The effects of annealing temperature on microstructure, insulating, ferroelectric and dielectric properties were characterized. The result reveals that 0.65PMN-0.35PT thin films possess a polycrystalline structure, matching well with the perovskite phase despite the existence of a slight pyrochlore phase. The film samples annealed at all temperatures exhibit relatively dense surfaces without any large voids and the grain size increases generally with the increase of the annealing temperature. Meanwhile, pyrochlore phase is considerably generated because of the deformation of perovskite phase caused by volatilization of Pb at an excessive high-temperature. The film annealed at 650 °C exhibits superior ferroelectricity with a remanent polarization (P_r) value of 13.31 μC/cm², dielectric constant (ε_r) of 1692 and relatively low dielectric loss (tanδ) of 0.122 at 10⁴ Hz due to the relatively homogeneous large grain size of 130 nm and low leakage current of approximately 10^-6 A/cm².     

Compressive mechanical properties of partially sintered porous alumina of bimodal particle size system

This paper examined theoretically and experimentally packing behavior, sintering behavior and compressive mechanical properties of sintered bodies of the bimodal particle size system of 80 vol% large particles (351 nm diameter)–20 vol% small particles (156 nm diameter). The increased packing density as compared with the mono size system was explained by the packing of small particles in 6-coordinated pore spaces among large particles owing to the similar size relation between 6-coordinated spherical pore and small particle. The sintering between adjacent large particles dominated the whole shrinkage of the powder compact of the bimodal particle size system. However, the bimodal particle size system has a high grain growth rate because of the different curvatures of adjacent small and large particles. The derived theoretical equations for the compressive strengths of both mono size system and bimodal particle size system suggest that the increase in the grain boundary area and relative density by sintering dominate the compressive strength of a sintered porous alumina. The experimental compressive strengths were well explained by the proposed theoretical models. The strength of the bimodal particle size system was high at low sintering temperatures but was low at high sintering temperatures as compared with that of mono size system of large particles. This was explained by mainly the change of grain boundary area with grain growth. The stress–strain relationship of the bimodal particle size system showed an unique pseudo-ductile property. This was well explained by the curved inside stress distribution along the sample height. The inside stress decreases toward the bottom layer. The fracture of one layer of sintered grains over the top surface proceeds continuously with compressive time along the sample height when an applied stress reaches the critical fracture strength.     

The development of metal hydrides using as concentrating solar thermal storage materials

Metal hydrides high temperature thermal heat storage technique has great promising future prospects in solar power generation, industrial waste heat utilization and peak load regulating of power system. This article introduces basic principle of metal hydrides for thermal storage, and summarizes developments in advanced metal hydrides high-temperature thermal storage materials, numerical simulation and thermodynamic calculation in thermal storage systems, and metal hydrides thermal storage prototypes. Finally, the future metal hydrides high temperature thermal heat storage technique is been looked ahead.     

Polarized light microscopy: utilization in the investigation of the recrystallization of aluminum alloys

To obtain specific properties and performance from a metallic material, it is necessary to control the microstructure. This imposes a need to monitor closely and/or predict microstructural transformations during downstream processing. One of the main features that determine the properties of wrought metals and alloys is the status of their matrix, which may be changed by thermomechanical treatment procedures. Different softening processes, such as recovery, recrystallization (RX) or grain growth, may occur in cold- and hot-worked materials. The present paper focuses on different aspects of RX and the microscopic methods used for its study. Examples of the usefulness of light microscopy examinations in the study of RX of several aluminum alloys are given.     

CO_2饱和的0.5mol/L NaCl溶液中温度对3Cr低合金钢腐蚀行为的影响

低合金钢在含CO2的NaCl溶液中的腐蚀行为受温度影响很大。利用动电位极化和电化学阻抗(EIS)技术研究了CO2饱和的NaCl溶液中温度对3Cr低合金钢腐蚀过程的影响。结果表明:温度的升高促进了腐蚀过程的阴阳极反应,合金钢的腐蚀速率增大;随着温度的升高,阳极塔菲尔斜率逐渐减小,阴极塔菲尔斜率逐渐增大,电极表面的阳极区面积逐渐增大,而阴极区面积逐渐减小;温度升高对阴极过程的促进作用大于阳极过程,使Ecorr发生正向移动;温度升高提高了合金钢的腐蚀速率,但极化曲线形状基本相同,即腐蚀机理未发生变化;合金钢在CO2饱和的0.5 mol/L NaCl溶液中的电化学阻抗谱均出现2个时间常数,高频和中频段出现由双电层界面电容和电荷转移电阻引起的容抗弧,低频段出现与钝化膜相关的容抗弧,但都随着温度的升高而减小。     

Effects of braiding angle on modal experimental analysis of three-dimensional and five-directional braided composites

In this paper, the experimental modal analysis of three dimensional (3D) and five (5)-directional braided composite cantilever beams with different braiding angle was conducted systematically with a simple testing system. Preforms were made by four-step 1 × 1 square integral braiding method. The first three order modes of composite specimens were derived, which are different with braiding angles. The experimental result and mechanism were discussed. Experimental observations and analytical predictions show that the natural frequency of specimens decreased and the damping ratio of specimens increased when the braiding angle increased. Furthermore, specimens with smaller braiding angle will be valuable for the better anti-exiting property, and have an opposite effect on dissipation of vibration energy. The comparison between the specimens with different braiding angles reveals that braiding angle is a crucial factor for the vibration performance design of 3D and 5-directional braided composites.     

Study on the effect of PbO on the passive behavior of alloy 690 in sodium hydroxide aqueous solution

The corrosion behaviors of alloy 690 in 1 wt pct sodium hydroxide aqueous solutions with and without PbO were characterized by electrochemical measurements, including potentiodynamic polarization, electrochemical impedance spectroscopy and Mott-Schottky measurement. The results reveal that there is a great difference between the corrosion behaviors of alloy 690 in the two tested solutions. The corrosion current density in PbO-containing solution is higher than that in the solution without PbO, which may be attributed to the anodic dissolution of metallic lead deposited at the early stage of polarization. The electrochemical impedance of the specimen in PbO-free solution is higher than that in the solution containing PbO. The slope of the Mott-Schottky curve in Pb-containing solution decreases notably compared with that in the Pb-free solution, which can be interpreted by the chromium depletion in the duplex structure of passive films.     

Effects of R2CO3 (R = Li,Na and K) on the reduction of MoO2 to Mo by hydrogen

In the present work, the influence of different factors (additives and temperatures) on the morphologies and sizes of as-prepared metal Mo powders by the hydrogen reduction of MoO₂ in the temperature range of 1053 K to 1353 K are investigated. When pure MoO₂ powders are reduced, the morphologies and sizes of as-prepared metal Mo powders are nearly kept the same as the raw materials. However, it is found that adding a small amount of additives (Li₂CO₃, Na₂CO₃ and K₂CO₃) into MoO₂ has a great influence on that of prepared metal Mo powders. The particles become uniformed, ultrafine and spherical powders. In addition, the particles size of the as-prepared metal Mo powders will become larger as the increase of reaction temperature due to the grains growth. This work provides a new method for the preparation of uniformed, ultrafine and spherical metal Mo powders.     

Highly ameliorated gaseous and electrochemical hydrogen storage dynamics of nanocrystalline and amorphous LaMg12-type alloys prepared by mechanical milling

Nanocrystalline and amorphous LaMg12-type alloy-Ni composites with a nominal composition of LaMg11 Ni+x wt.% Ni (x=100, 200) were synthesized via ball milling.The influences of ball mill-ing duration and Ni adding amount x on the gaseous and electrochemical hydrogen storage dynamics of the alloys were systematically studied.Gaseous hydrogen storage performances were studied by a differential scanning calorimeter and a Sievert apparatus.The dehydrogenation activation energy of the alloy hydrides was evaluated by Kissinger method.The electrochemical hydrogen storage dynam-ics of the alloys was investigated by an automatic galvanostatic system.The H atom diffusion and ap-parent activation enthalpy of the alloys were calculated.The results demonstrate that a variation in Ni content remarkably enhances the gaseous and electrochemical hydrogen storage dynamics perform-ance of the alloys.The gaseous hydriding rate and high-rate discharge (HRD) ability of the alloys ex-hibit maximum values with varying milling duration.However, the dehydriding kinetics of the alloys is always accelerated by prolonging milling duration.Specifically, rising milling time from 5 to 60 h makes the hydrogen desorption ratio (a ratio of the dehydrogenation amount in 20 min to the saturat-ed hydrogenation amount) increase from 57% to 66% for x=100 alloy and from 57% to 70% for x=200.Moreover, the improvement of gaseous hydrogen storage kinetics is attributed to the descending of dehydrogenation activation energy caused by the prolonging of milling duration and growing of Ni content.