镁及其合金表面化学镀银工艺的研究

研究了镁合金表面化学镀银的工艺:利用涂膜及化学镀的方法对镁合金进行处理,即先在镁及其合金表面涂覆有机涂膜,然后再进行化学镀.工艺利用有机涂膜充当基体镁合金与镀层之间的中间层,使基体与镀层之间不直接接触,当化学镀进行时,镀层直接在中间层表面形成.虽然镁的化学活性高,但中间层的存在使化学镀银可以在镁及其合金表面实现.以AZ31镁合金轧板为基体,采用该工艺在其表面得到了理想的银镀层.通过SEM和XRD分析了银镀层的生长过程.十字切割法测量结果表明,涂膜与基体之间的结合力能满足使用要求.用极化曲线法研究了化学镀后试样在NaCl溶液中的腐蚀行为,结果表明:化学镀后试样的自腐蚀电位明显正移,腐蚀电流远远小于基体,具有良好的耐蚀性.     

Al2O3/Ti6Al4V diffusion bonding joints using Ag–Cu interlayer

Ceramic materials, such us alumina, are widely used for wear resistant and industrial components as in aircraft applications. On the other hand, Ti6Al4V is commonly used for aeronautical applications, due to its superplasticity, low weight and high mechanical resistance but has poor wear resistance because of its low resistance to plastic shearing. For these reasons numerous techniques have been developed to improve its wear resistance including joining to ceramic materials. Ceramics and alloys can be joined by several different processes and the use of an interlayer can further facilitate this process. In the present work Al₂O₃ and Ti6Al4V alloy have been diffusion bonded using a (Ag–Cu) interlayer. Identification of intermetallic phases formed within the bonded region enables the mechanical behaviour of the joints to be explained. These intermetallic phases are related to the bonding conditions applied (750 °C, 3 MPa with bonding times varied from 10 to 60 min).     

富县Y64区储层非均质性研究

通过露头剖面、岩心、样品分析及测井等资料对富县Y64区延长组长6段储集砂体分析表明,区内长6段低孔低渗砂体的非均质性强,不同小层存在差异。垂向上,长63至长61的非均值性逐渐增强;平面上各小层非均质性随着砂体变厚总体上有增大的趋势。     

The role of an SiC interlayer at a graphite–silicon liquid interface in the solution growth of SiC crystals

SiC crystal growth using the top seeded solution growth (TSSG) method involves the precipitation of solid SiC from carbon that is dissolved in a silicon melt. The growth rate of SiC is strongly influenced by the solubility of C in liquid Si, which is quite low. In this study, the dissolution of C from graphite to the Si melt was explored by observing the formation of an SiC interlayer at a graphite – Si liquid interface. The SiC interlayer was observed to become thickened during the several hours needed to reach a certain thickness at 1500 °C. Assuming that the SiC interlayer is a direct C source, a pre-formed SiC layer was coated on the graphite crucible to evaluate its effect on the concentration of C in the Si melt. As a result, the concentration of C in the Si melt increased within a short time, especially at low temperatures. By applying the SiC coated crucible to the TSSG process for SiC crystal growth, we confirmed that the development of a pre-formed SiC layer enhanced the growth rate of SiC crystals, especially at the initial stage of crystal growth at low temperatures.     

FTIR analyses of water in MX-80 bentonite compacted from high salinary salt solution systems

The effect of the exchangeable cations on the infrared (IR) spectra of water in MX-80 bentonite compacted from high salinary salt solution systems was studied using self-supporting film and attenuated total reflection (ATR) techniques. Na-bentonite MX-80 was saturated with homo-cationic (NaCl, KCl, CaCl₂ or MgCl₂) or hetero-cationic (mixtures of Na–, K–, Ca– and Mg–chlorides) solutions. The specimens for IR spectroscopy were prepared as self-supporting films (ssf) or compacted pastes. Differences in the wavenumbers and intensities of the structural OH group vibrations in relation to the type of the interlayer cation were found in the spectra of heated ssf. The most pronounced changes were observed for Mg-ssf, while only negligible changes occurred for K-ssf. The absorptions of water in heated Na- and K-ssf showed displacement of the stretching and bending bands to higher and lower wavenumbers, respectively, which indicates decreasing strength of H-bonding between water molecules. In contrast, for Mg-ssf the position of the stretching band of water substantially decreased on heating up to 90 °C followed by an increase upon further heating above 100 °C. The origin of these differences was discussed in terms of variations in the polarising ability of the interlayer cations influencing their hydration number. The ATR spectra of homo-cationic clay-pastes showed that the interlayer cations modify both the position and the intensity of the complex water band near 3400 cm⁻¹. The position decrease and the intensity increase followed the same order: K⁺, Na⁺, Ca²⁺, Mg²⁺. Good correlation between water band position and polarising power of the cations confirmed their influence on the strength of hydrogen bonds between water molecules. Similarly, a systematic shift of the H₂O-stretching band to lower frequencies with the increasing Mg²⁺ content in the samples was observed in the spectra of clay-pastes saturated with hetero-cationic chloride solutions. The intensity of the stretching band of water of both homo- and hetero-cationic pastes correlated very well with the water content obtained gravimetrically.     

Photoluminescence mechanism of annealed ZnO/Zn/Al2O3 sandwich structures deposited on glass substrates

ZnO/Zn/Al₂O₃ sandwich structures are grown on glass substrates by magnetron sputtering. The effect of Al₂O₃ layers on optical properties of ZnO/Zn/Al₂O₃ sandwich structures is investigated. Results indicated that as the deposition time of Al₂O₃ increases, violet peak centered at 402 nm gradually shifted to 412 nm and the intensity firstly decreases and then increases. We discuss the intensity change and shift of violet peak relating to V_Zn defects and the band alignment of ZnO/Zn/Al₂O₃ sandwich structures, respectively. We proposed that ZnO/Zn/Al₂O₃ sandwich structures can be approximately regarded as a quasiquantum-well-like structure. So the electron tunneling from Zn to Al₂O₃ layer is suppressed and the photogenerated carriers can be confined in the Zn Fermi level. In order to further understand the effect of posttreatment on optical properties of samples, samples are annealed in vacuum at 350 °C for 1 h. PL emissions are weakened with the increase of Al₂O₃ deposition time. Interestingly, at a same deposition condition, PL emissions are still improved after posttreatment. Combined Al₂O₃ layer modulation with annealing treatment, steady PL properties can be effectively improved.     

Influence of interlayer cations on the water sorption and swelling–shrinkage of MX80 bentonite

The potential of water sorption and swelling–shrinkage in the expansive clays is practically defined by the nature of interlayer cations. The purpose of this paper is to estimate the effects of the cation saturation (Mg⁺, Ca⁺, Li⁺, Na⁺, and K⁺) on the swelling–shrinkage behaviour of the MX80 bentonite.The MX80 bentonite (a “commercial clay”) was treated with concentrated solutions (1 N) of sodium, calcium, magnesium, potassium, and lithium chlorides. This treatment was made three times with constant agitation for 1 h. Then, the clay was washed three times with distilled water. The scanning transmission electron microscopy (STEM) and inductively coupled plasma atomic emission microscopy (ICP-AES) analyses were used to verify the efficiency of the cation saturation.Finally, two techniques were employed to estimate the effect of the cation saturation on the swelling–shrinkage behaviour of the bentonite: the first one uses an isothermal system of water adsorption, where the water activity is controlled by a supersaturated salt solution. In the second, environmental scanning electron microscopy (ESEM), coupled with a digital image analysis (DIA) program, was used to estimate the swelling–shrinkage potential at different water activities. The swelling–shrinkage isotherms were always estimated on isolated aggregates.The isotherms of water adsorption and swelling–shrinkage of the bentonite MX80 show that the amount of adsorbed water and the swelling–shrinkage potential depend directly on the interlayer cation. For example, the sodium bentonite presents an excellent capacity to swell while the lithium bentonite does not swell significantly at the aggregate scale. In addition, other textural properties may be modified by the cation saturation, such as the specific surface, the particle size, porosity, etc.     

Oscillatory interlayer magnetic coupling and induced magnetism in Fe/Nb multilayers

We present an ab initio calculation of interlayer magnetic coupling for Fe/Nb multilayers using the self-consistent full-potential linearized augmented-plane-wave (FLAPW) method. For this calculation, we have constructed supercells consisting of bcc Fe and Nb multilayers in Fe/Nb/Fe sandwich geometry stacked along (001) direction. In the supercells two Fe layers are separated by Nb layers ranging from 1 to 11 layers. We have calculated the total energy of the system as a function of Nb spacer layer thickness. For each spacer layer thickness, we have done three calculations corresponding to para, ferro and antiferromagnetic ordering of Fe atoms. The interlayer magnetic coupling is obtained from the energy difference of the systems in which Fe layers are antiferromagnetically and ferromagnetically ordered. We find that the interlayer magnetic coupling oscillates with increasing Nb spacer thickness in agreement with the experimental results. The induced magnetic moment is also found to be oscillating with increasing Nb spacer layer thickness.     

Effect of interlayer addition on microstructure and mechanical properties of NiTi/stainless steel joint by electron beam welding

NiTi/Stainless Steel(SS) sheets have been welded via a vacuum electron beam welding process, with three methods(offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding Fe Ni interlayer), to promote mechanical properties of the Ni Ti/SS joints. The joints with different interlayers are all fractured in the weld zone near the Ni Ti side, which is attributed to the enrichment of intermetallic compounds including Fe2 Ti and Ni3 Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding Fe Ni interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2 Ti, Ni3 Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3 Ti and Fe2 Ti will be formed when the Fe Ni alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa.