Fabrication of poly(ε‐caprolactone) (PCL)/poly(propylene carbonate) (PPC)/ethylene‐α‐octene block copolymer (OBC) triple shape memory blends with cycling performance by constructing a co‐continuous phase morphology

In this paper, a triple shape memory material was prepared by ultra‐simple melt blending from poly(ε‐caprolactone) (PCL), poly(propylene carbonate) (PPC) and ethylene‐α‐octene block copolymer (OBC). The obtained material possessed a co‐continuous phase morphology and presented an excellent triple shape memory effect (triple‐SME). Theoretical prediction demonstrated that a special continuous phase morphology could be constructed by adjusting the proportions of the blend. Moreover, the results indicated that a close relationship existed between the phase morphology and the triple‐SME of PCL/PPC/OBC. The sample with 35 vol% PPC content contributed to the formation of a continuous phase morphology and exhibited the optimal triple‐SME. Additionally, the sample PCL/PPC/OBC (32.5/35/32.5) showed outstanding structure and performance stability during cycle loading–unloading tests, which evidenced the prominent cycling shape memory property (nearly 100% shape fixing and recovery of temporary shape). Overall, this work could provide an efficient, convenient and recyclable method to obtain high‐performance shape memory materials. © 2020 Society of Chemical Industry     

高Cu含量Al-Cu-Li-Sc合金中W(Al8Cu4Sc)相的形成机制

采用光学显微镜(OM)、扫描电镜(SEM)、电子探针显微分析(EPMA)、X射线衍射(XRD)以及扫描透射电镜(STEM),研究了一种高Cu含量Al-2.35Cu-4.6Li-0.12Sc(at%)合金在均匀化热处理过程中微观组织演变以及W(Al₈Cu₄Sc)相的形成机制。结果表明:铸态时,合金中的主要凝固相为T_B(Al₇Cu₄Li)相,Sc主要以过饱和固溶体的形式存在于基体中;均匀化后,T_B相完全溶解,基体中的Cu含量增加,Sc含量减少,稳定的W相形成。分析表明,由于T_B相与基体界面是非共格的,W相优先在此界面形核将有利于其形核能的降低。W相形核后通过不断消耗其附着的T_B相上的Cu原子和Al基体中的过饱和Sc原子而逐渐长大,直至形成尺寸1 μm左右的稳定粒子。     

FeCrAl不锈钢包壳管挤压及退火工艺优化

利用光学显微镜、扫描电镜、电子背散射衍射和万能拉伸试验机等对FeCrAl合金包壳管挤压前后的微观组织、析出相及退火后的微观组织、析出相、再结晶及力学性能进行了研究。结果表明:Nb含量对FeCrAl合金中第二相的析出影响显著,高Nb含量下Laves相的析出温度和析出数量均大大提高;降低挤压温度有助于FeCrAl合金管坯中形成细小弥散第二相;随着退火温度升高,细小弥散相的析出数量呈现先增多后减少的趋势;在相同退火工艺下,800 ℃热挤压管坯的室温力学性能比950 ℃热挤压管坯的室温力学性能要更加优异。     

Review of the phase change material (PCM) usage for solar domestic water heating systems (SDWHS)

The shortage in energy resources combined with the climb in greenhouse emissions is the main incentive beyond the deployment of solar energy resource in various applications. One of the most successful applications is the utilization of solar energy in the domestic water heating systems (DWHS) because 70% of the consumed energy in the residential segment is utilized for space heating and appliances in cold climates 1 . However, the full deployment of solar energy in domestic water heating is only possible when an energy storage system with acceptable price is available. Recently a new tendency for deploying phase change materials (PCMs) as an energy storage system is introduced in several solar DWHS. These systems are known as integrated PCM in solar DWHS and offer several advantages including high storage capacity, low storage volume, and isothermal operation during the charging and discharging phases. The present study reviews various techniques utilized for integrating the PCM in solar water heating systems and the utilized methods for enhancing the heat transfer characteristics of the PCM through the usage of extended surfaces and high conductive additives. Copyright © 2017 John Wiley & Sons, Ltd.     

基于复合相变材料的梯级组合蓄热特性研究

针对潜热蓄热装置内部相变材料（PCM）导热系数偏小，蓄热速率过低的问题，对基于复合相变材料的两级串联式梯级蓄热装置的相变过程进行了数值研究。通过对不同热物性PCM工况的对比与分析，得到了装置在不同工况下的蓄热特性。结果表明，存在最佳的热扩散系数，使固定熔点的PCM实现“均匀等速相变”。同时，增大PCM的热扩散系数可以有效降低加热面温度，但随着热扩散系数的增大，加热面温度降低幅度减小。通过分析Stefan数，得到了装置最佳的参数，使工况蓄热效果最佳。最后，通过Stefan数为2.88时的实验工况验证了相关规律的正确性。     

纳米级超声造影剂的理论研究进展

为了克服超声造影剂中微米级气泡尺寸较大的局限性,大量研究人员对超声应用的替代造影剂(纳米级造影剂)进行了研究。随着生物纳米技术的飞速发展,纳米级超声造影剂在诊断与治疗领域有着广阔的发展前景。与超声造影剂中的微米级气泡相比,纳米级造影剂粒径较小,渗透能力极强,可以通过血管内皮间隙,进而可以实现血管外病变部位的显影。文中详细论述了超声造影剂在超声作用下的行为以及2种主要的纳米级造影剂:纳米气泡和纳米液滴造影剂,对其理论研究进展进行了总结,并提出了目前仍存在的一些问题及其未来的研究方向。     

Corrosion behaviour of Mg-Gd-Y-Zn-Ag alloy components with different sizes after cooling

The corrosion behaviour of Mg-6Gd-3Y-1Zn-0.3Ag (wt.%) alloy components with different sizes after cooling was investigated. The alloys in the small components (SC) cooled fast, which were composed of α-Mg matrix and coarse long-period stacking ordered (LPSO) phases. The alloys in the large components (LC) cooled slowly, and there were thin lamellar LPSO phases precipitating inside the grains, except for α-Mg matrix and coarse LPSO phases. The hydrogen evolution test revealed that the corrosion rate of LC sample was higher than that of SC sample. Electrochemical impedance spectroscopy (EIS) test showed that the surface film on LC alloys provided worse protection. The corrosion morphologies indicated that the precipitation of the thin lamellar LPSO phases in LC sample caused severe micro-galvanic corrosion, which accelerated the rupture of the surface film.     

Crystal structure,polarization properties and reverse nonlinearity of solid solutions of the KNN-PZT system in a wide range of external influences

Experimental research of the crystal structure, polarization properties, and reverse nonlinearity of ceramic solid solutions of the (1-x) (Na_0·5K_0.5)NbO₃-xPb(Ti_0·5Zr_0.5)O₃ (KNN-PZT) quasi-binary system with 0.0 = x ≤ 1.0 in a wide range of external influences (temperatures, strength of dc/ac fields) has been done. Based on the X-ray structural data, an x-T diagram of the system has been constructed, and correlations of the behavior of the macroproperties of solid solutions with the features of their phase states with the temperature change have been established. It has been concluded that it is advisable to use the proposed compositions when designing microelectronic devices operating in various extreme conditions.     

利用菊池衍射花样鉴定晶体结构的方法研究

电子背散射衍射(Electron Backscatter Diffraction, EBSD)是研究材料显微结构的重要手段之一, 通过EBSD获取的菊池衍射花样是材料内部微观晶体结构的直观反映。本研究通过识别菊池花样中的对称轴, 结合晶体对称定律, 提出了一种利用菊池花样进行晶体对称性分析和晶体结构鉴定的方法。通过该方法成功对三个未知样品的对称性和晶体结构进行了判断。其中一个样品确定到所属晶系, 另两个样品锁定到部分点群, 通过确定晶系和点群排除了部分不符合对称性的相鉴定结果。研究结果表明, 利用菊池花样进行对称性分析是判断晶体结构的有效方法。同现有方法相比, 菊池衍射花样法大大缩小了相鉴定的检索范围, 显著提高了相鉴定的准确性和可靠性, 是一种有望用于新一代EBSD设备的标定技术。     

Characterization of the structure and properties of processed alumina-graphene and alumina-zirconia composites

The onset of hybrid alumina-based composites, which combines two or more nano-particles within the alumina matrix has already shown promising improvements in the matrix material. However, variations in mechanical properties including the optimum compositions that give improved properties faced with the development of alumina-based composites require further studies to understand the underlying mechanisms and synergistic effects of the nano-particle additions on the alumina matrix. In the current study, the structure and properties of Al?O?-graphene (0.5 wt%) and Al?O?–ZrO? (4 wt% and 10 wt%) composites fabricated via hot-pressing was studied as a baseline for multiple combinations. Even though the addition of 10 wt%ZrO? resulted in a 23% reduction in the grain size of the alumina matrix, the 4 wt%ZrO? addition resulted in a 14% increase in grain size as compared to the parent alumina matrix. X-ray diffraction analysis revealed that there was approximately 85% monoclinic (m-ZrO₂) vs. 15% tetragonal (t-ZrO₂) crystal structures in the A4ZrO? sample whilst the A₁₀ZrO? had approximately 93% m-ZrO₂ vs. 7% t-ZrO₂. The high-volume fraction of the monoclinic crystal structures in the A₁₀ZrO? accounts for the induced microcracks in the sample since the transition from the ductile-tetragonal to brittle-monoclinic is associated with the exertion of compressive stresses on the alumina matrix by the associated elastic volume expansion of m-ZrO₂. Also, the addition of 0.5 wt%graphene resulted in about 37% reduction in the grain size of the alumina matrix, and approximately 10% increase in hardness as a result of the distribution of graphene along the grain boundaries of the parent alumina matrix, which restricts grain coalescence and growth during processing. Furthermore, an increase up to 115% and 164% were observed in the fracture toughness (K_IC) with the inclusion of 0.5 wt%graphene and 10 wt%ZrO? respectively, which was primarily ascribed to the fine-grained microstructures and toughening mechanisms of the intergranular graphene and ZrO? particles.