Threshold Chloride Concentration for Passivity Breakdown of Mg-Zn-Gd-Nd-Zr Alloy (EV31A) in Basic Solution

Mg-Zn-Gd-Nd-Zr alloy(EV31A) is a heat-treatable magnesium(Mg) cast alloy that can be used up to 200 ℃for automobile and aerospace applications.This alloy has excellent mechanical properties(ultimate tensile strength:280 MPa at room temperature,and ~ 230 MPa at 200 ℃) and improved corrosion resistance.Electrochemical corrosion studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of0-1000 ppm of chloride.The alloy showed excellent passivity in the 0.1 M NaOH solution.The passive potential range typically extended to more than 1.2 V_(Ag/AgC1).The transpassive potential was observed to be dependent on heat treatment condition of the alloy.More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition.Peak aging at 200 ℃ for 16 h imparted better resistance for localized corrosion than other heat-treated conditions.The alloy in the as-received condition showed the highest passivation kinetics due to its smaller grain size that possibly increased the diffusion of reactive elements to form protective oxide.The passive film of the EV31 A alloy showed n-type semiconductivity with a charge carrier density of ~2×10~(21) cm~(-3) with no chloride addition.The charge carrier density increased with chloride addition in the electrolyte which could be correlated with the susceptibility to localized corrosion.     

Modification of the Recovery Behavior of TiNi Shape Memory Alloy （SMA） by Chemical Heat Treatment

In order to improve the linear recovery behavior, TiNi shape memory alloy springs were samariumed at 550℃ for 4 hours with SmH3 as samarium source, in a vacuum furnace. The phase of samariumed layer was determined by X-ray diffractometer (XRD). The fracture surface of TiNi SMA spring was investigated by scanning electronic microscope (SEM), The experimental results indicate that a 2μｍ thick samariumed layer composed of NiSm intermetallics existed on the fracture surface. Additionally, a new idea of linear recovery behavior in shape memory alloy (SMA) has been proposed, and its properties have been defined. The reversion measurements show that the linear recovery properties of TiNi SMA were obviously improved. The temperature range of the linear reversion (Tw) was enlarged from 4℃ to 8℃, The ratio of linear reversion (η) was increased from 54% to 75%, the proportion of linear reversion (PL) was increased from 56% to 70%, and the proportion of non-linear reversion (Ps) was decreased from 44% to 10%, but the proportion of total reversion (PT) has a little decrease. These results were attributed to the strengthening effect of NiSm intermetallics.     

Effects of Heat Treatment and Thermal Cycling on Martensitic Transformation Behavior of Ni59Al11Mn30 High Temperature Shape Memory Alloy

A reversible martensitic transformation (MT) takes place during cooling and heating in the solution quenched and the solution quenched plus aged Ni59Al11Mn30 alloy. The MT temperature increases with increasing solution temperature. The excellent MT characteristics can be obtained from a process of 1000℃ solution quenched plus 400℃ aged. Follow this process, the MT start temperature (Ms) and the reverse MT finish temperature (Af) are 469℃ and 548℃,respectively. The martensitic stabilization effect in the solution quenched and aged Ni59Al11Mn30 alloy is observed as an increase in the Af temperature of the first reverse MT during thermal cycles. This stabilization effect vanishes from the second thermal cycle. Thermal cycling can enhance the stability of the reversible MT. The microstructure of the quenched Ni59Al11Mn30 alloy consists of martensite (M) and gamma phase. The volume fraction of gamma phase is about 40%. The substructure of M and gamma phase is twins and dislocations, respectively. The hardness of M is higher than that of gamma phase. After aging treatment the basic phases of alloy do not change, but the hardness of the phases increases.     

聚合物冷却介质和热处理冷却技术(二)

冷却技术是热处理中的重要和关键问题。聚合物冷却介质的应用和发展与冷却技术紧密相关。概要介绍PVA、PAG、PSA、PVP、PEOX、PEG、PMI和PAM等聚合物冷却介质及它们对冷却机理的影响。最后阐述聚合物冷却介质的维护。     

聚合物冷却介质和热处理冷却技术(一)

冷却技术是热处理中的重要和关键问题。聚合物冷却介质的应用和发展与冷却技术紧密相关。概要介绍PVA、PAG、PSA、PVP、PEOX、PEG、PMI和PAM等聚合物冷却介质及它们对冷却机理的影响。最后阐述聚合物冷却介质的维护。     

有机大阳离子与HnXW12O40·nH2O（X=B，Si，P）多金属氧酸盐的合成及热行为

合成了3种新的多金属氧酸盐(CTMA)5BW12O40·8H2O,(CTMA)4SiW12O40·3H2O,(CTMA)3PW12O40·2H2O,利用元素分析、IR光谱和TG-DTA技术对其进行了表征.IR光谱表明这些化合物不仅含有Keggin型结构,而且存在有机大阳离子的特征吸收峰;TG-DTA曲线显示它们的热行为是一个多步分解过程,首先这些化合物在大约269℃以下脱去水分子,然后它们的无水多金属氧酸盐经历了两步或3步的分解过程,分别脱去CTMA分子及其碎片,并伴随Keggin型结构的塌陷.通过XRD和IR光谱确证其最终分解产物是一个含有WO3与B2O3,SiO2或P2O5的混合物.同时还提出了这些化合物可能的热分解过程.     

半固态A356合金触变铸造流变特性的研究

研究在压铸环境下,二次加热温度为570～580℃时,半固态铝合金触变铸造的流变特性。剪切速率在2×(103～104)s-1范围,半固态铝合金触变铸造过程呈现为伪塑性流体流变特性;当剪切速率大于106 s-1时,半固态铝合金触变铸造的流变特性为涨塑性;获得了基于幂定律的半固态铝合金(A356)触变铸造过程的流变方程以及由此得到的粘度模型。     

改性竹炭对银（I）的吸附性能与机理

研究了改性竹炭对银(I)的吸附性能与机理.研究表明:竹炭对银(I)有良好的吸附性能,平衡吸附量为45.2 mg/g;竹炭对银的吸附动力学可用准一级动力学描述,表观吸附速率常数k298=3.29×10-4 s-1,表观吸附活化能为:Ea=36.1 kJ·mol-1;银在竹炭上的吸附符合Langmiur吸附等温线,吸附系数KL(298 K)为24.427 L·mg-1,饱和吸附量Q∞为62.7 mg/g;温度升高,吸附量减小,表明吸附为放热过程;测得吸附热力学参数为:ΔH= -40.9 kJ·mol-1,ΔG=-36.6 kJ·mol-1,ΔS=-14.46 J·K-1·mol-1.机理研究表明:竹炭对银(I)的吸附主要为还原吸附.     

Use of Electrochemical Noise (EN) Technique to Study the Effect of sulfate and Chloride Ions on Passivation and Pitting Corrosion Behavior of 316 Stainless Steel

In the present paper, studies were conducted on AISI Type 316 stainless steel (SS) in deaerated solutions of sodium sulfate as well as sodium chloride to establish the effect of sulfate and chloride ions on the electrochemical corrosion behavior of the material. The experiments were conducted in deaerated solutions of 0.5 M sodium sulfate as well as 0.5 M sodium chloride using electrochemical noise (EN) technique at open circuit potential (OCP) to collect the correlated current and potential signals. Visual records of the current and potential, analysis of data to arrive at the statistical parameters, spectral density estimation using the maximum entropy method (MEM) showed that sulfate ions were incorporated in the passive film to strengthen the same. However, the adsorption of chloride ions resulted in pitting corrosion thereby adversely affecting noise resistance (R _N). Distinct current and potential signals were observed for metastable pitting, stable pitting and passive film build-up. Distinct changes in the values of the statistical parameters like R _N and the spectral noise resistance at zero frequency (R°_SN) revealed adsorption and incorporation of sulfate and chloride ions on the passive film/solution interface.     

Synergistic Extraction of Rhenium(VII) and Molybdenum(VI) with Mixtures of Bis-(3,5-dimethylhexyl-4-methylhexyl) Amine and Tributylphosphate

The extraction of rhenium(VII) and molybdenum(VI) from chloride media by mixtures of bis-(3,5-dimethylhexyl-4-methylhexyl) amine N298 and tributylphosphate (TBP) was studied in the present paper. The mixtures had higher synergistic effects on Re(VII) than that of Mo(VI), and the maximal synergistic factor was obtained at a ratio of N298 to TBP of 1 to 9. Re(VII) was extracted as (R₂NH₂Cl)₃·HReO₄·B, whereas Mo(VI) was extracted as (R₂NH₂Cl)_1/2·H₂MoO₄·1/4B by the mixtures, instead of (R₂NH₂Cl)₃·HReO₄ and (R₂NH₂Cl)₃·H₂MoO₄ by N298 alone. Furthermore, the formation constants and extraction mechanism were determined. The possibility of separating rhenium and molybdenum ions by the mixtures according to its synergistic effects and extraction ability was investigated.     

汽车发动机用AZ31镁合金的合金化与热处理行为研究

对汽车发动机用AZ31镁合金进行了微合金化和固溶时效处理,研究了不同稀土添加量对铸态和固溶时效态AZ31合金力学性能与显微组织的影响。结果表明,在AZ31合金中添加0.76%的稀土时,合金可以获得较好的室温和150℃高温力学性能,这是因为合金的晶粒细化和第二相的析出强化作用。     

Aqueous Corrosion Behavior of Micro Arc Oxidation (MAO)-Coated Magnesium Alloys: A Critical Review

Magnesium (Mg) and its alloys, in the current era of persistently growing engineering demands, have become the most promising materials finding widespread industrial applications. Numerous processes are available for surface protection of Mg and its alloys to potentially minimize corrosion damage. The micro arc oxidation (MAO), a fairly recent and eco-friendly coating process, emerged as a novel means to provide an adherent, hard, scratch-resistant, wear-resistant, and corrosion-resistant coatings on Mg alloys. However, the successful utilization of such coatings demands a thorough understanding of the influence of a relatively large number of process parameters such as electrolytic composition, presence of insoluble additives in the electrolyte, electrical parameters employed, and the composition of the Mg alloy substrate on the corrosion resistance. The detailed influence of all the above parameters on the corrosion behavior of Mg alloys is critically reviewed and presented in this article. In addition, this article also reviews the recent trends in terms of duplexing the MAO process using different techniques/processes such that the composite coatings are produced with enhanced corrosion resistance.     

消失模铸造用EPMMA模样的收缩特性

以可发性聚甲基丙烯酸甲酯(EPMMA)模样为研究对象，系统研究了珠粒粒径、预发泡时间、预发泡珠粒熟化时间、成形蒸气压力、模样的贮存温度及放置时间对模样收缩率的影响。研究结果表明，EPMMA模样在脱模时大约有0．1％左右的收缩，此后随着模样放置时间的延长，模样收缩逐渐增大，并在一定的时间(室温贮存约30天，50℃贮存约15天)后收缩稳定在0.5％～0．6％。而在所研究的工艺因素中，以成形蒸气压力对模样收缩的影响最大，其次是预发泡珠粒熟化时间，而珠粒粒径和预发泡时间的影响则相对较小。     

PVA对凝胶注模成型的悬浮体和坯体性能的影响

研究了采用新体系的陶瓷悬浮体的分散性、流变行为、固化特性以及坯体的抗弯强度.     

In situ Formed Fan-Shaped Nanowires in Biomorphic SiO_2:A Multidimensional Composite of Hierarchical Porous Material and Organic Pollutant Adsorption Behavior

Fan-shaped SiO_2 nanowires modified SiO_2@C composites with a bio-inspired hierarchical porous structure and a high accessible surface area were prepared by in situ molten salt template method.The combination of biogenic hierarchical porous structure and one-dimensional nanostructure with similar features was successfully obtained by one-pot heat treatment in the presence of rice husk SiO_2 with SiO_2 acting as precursor and ZnCl_2 acting as molten salt and growth template.A large amount of fan-shaped SiO_2 nanowires with numerous tiny branches sprouting from the central nanowires were grown in the inter-porous epidermis and on the surface of rice husk SiO_2 for temperatures up to 1200 °C.The in situ ZnCl_2 molten salt template base-growth mechanism is responsible for the initial formation of SiO_2/ZnCl_2 co-melting nanowires and the subsequent growth of fan-shaped SiO_2 nanowires.The as-prepared samples have been successfully employed as organic absorbers with high efficiency in the field of wastewater treatment.     

磷酸三乙酯与稀土铈(Ⅳ)离子在盐酸溶液中对Cu的缓蚀协同效应

采用电化学阻抗和动电位极化曲线研究了磷酸三乙酯(TEP)对Cu在0.5 mol/L盐酸溶液中的缓蚀作用,考察了TEP与稀土Ce4+对Cu在0.5 mol/L盐酸溶液中的协同作用。结果表明,在TEP浓度不变的情况下,随着Ce4+浓度的增加,缓蚀率先增后减,当Ce4+浓度为1.0 mmol/L时,缓蚀效果最好。在Ce4+浓度不变的情况下,随着TEP浓度的增加,缓蚀率逐渐增大。当复配缓蚀剂浓度为1 mmol/LCe4++58.7 mmol/L TEP时,其缓蚀率达到最大,为80.6%。     

Mg_(80)Cu_(15)Y_5合金的非晶形成能力及晶化行为

采用单辊快速凝同法制备出厚约40μm的Mg_(80)Cu_(15)Y_5非品合金薄带,利用XRD、DSC、TEM和HRTEM研究了非品合金的非品形成能力和晶化行为,分析了品化对合金组织结构与性能的影响.结果表明:Mg_(80)Cu_(15)Y_5合金的过冷液态温度区间△T_x和约化玻璃转变温度T_(rg)分别为55K和0.58,表明其具有较强的非晶形成能力;该合金在退火温度高于473 K后发牛明显晶化,从非品基体中析出 Mg_2Cu、Cu_2Y和Mg晶体相;随着退火温度的升高,合金的硬度呈现出先升高后降低的变化趋势,这与纳米品体相颗粒的弥散析出、重溶及粗化有关.     

Organic metals and semiconductors: The chemistry of polyacetylene, (CH)x,and its derivatives

Polyacetylene, (CH)_x, is the simplest organic polymer. Both the cis- and trans-forms may be prepared as silvery, flexible, polycrystalline, semiconducting films. The cis-films can be stretched to over three times their original length with partial alignment of the (CH)_x fibrils. Through chemical or electrochemical doping, the electrical conductivity of the films can be increased over twelve orders of magnitude with properties ranging from insulator (σ < 10^?10 ohm^?1 cm^?1) to semiconductor, to metal (σ > 10³ ohm^?1 cm^?1). By the use of donors or acceptors, n-type or p-type polymer, respectively, is produced. When doped, the partly aligned (CH)_x film shows marked anisotropic electrical and optical properties. The more chemically oriented aspects of (CH)_x and its derivatives and those physical studies which are most illustrative of the effects of doping will be discussed.