AZ91-0.75Ce稀土镁合金差热分析及β相形成规律

采用真空感应熔炼方式,研究了稀土元素Ce对AZ91镁合金铸态组织的影响。利用差热分析仪,通过对稀土镁合金熔化和凝固过程进行实时分析,研究了不同冷却速率(10、20、40和80℃/min)条件下β相的形成规律。结果表明,稀土元素Ce有利于细化AZ91合金的基体组织,同时形成Al-Ce化合物相,有效抑制晶界处β-Mg17Al12离异共晶相的形成。此外,Ce含量为0.75%的AZ91合金导致其液相线温度由605℃下降到583℃。近平衡凝固条件下,随冷却速率提高,液固界面前沿溶质扩散不及时,热分析曲线中共晶峰的相对面积不断增加,β共晶相含量逐渐升高。由于冷速的增加缩短了固态相变时间,导致共析转变过程中所形成的层片状β相含量降低。     

Ligand-free Au nanoclusters/g-C3N4 ultra-thin nanosheets composite photocatalysts for efficient visible-light-driven photocatalytic H2 generation

In this paper, we report the synthesis of ligand-free Au nanoclusters (NCs)/g-C₃N₄ ultra-thin nanosheets (NSs) composite via a facile wet-impregnation method with post-annealing. On the one hand, post-annealing was used for the exfoliation of multi-layered g-C₃N₄ to obtain ultra-thin NSs; on the other hand, after Au₂₅(Cys)₁₈ NCs were loaded, post-annealing was further adopted to remove the ligands to obtain clean surface on Au NCs. It is demonstrated that the loaded Au NCs were aggregating resistant by post-annealing. Constructing heterojunctions with appropriate inter-band structures between the ligand-free Au NCs and the ultra-thin g-C₃N₄ NSs, along with the mono-distribution of the Au NCs and their intimate contact with g-C₃N₄ NSs ensured the smooth interfacial charge transfer. As a result, the composite photocatalysts exhibited efficient visible-light-induced photocatalytic H₂ generation, mainly due to the local electric field enhancement induced by excitation of Au NCs under visible light and the improved charge separation in g-C₃N₄. This work provides a general strategy for the synthesis of noble metal NCs based composites with clean surface as the efficient photocatalysts for solar energy conversion.

Graphical Abstract

A stepwise post-annealing strategy is exploited to prepare g-C₃N₄ ultra-thin nanosheets modified with highly dispersed ligand-free Au nanoclusters for efficient photocatalytic hydrogen production.

     

Boosting the Electrical Double‐Layer Capacitance of Graphene by Self‐Doped Defects through Ball‐Milling

Improving the capacitance of carbon materials for supercapacitors without sacrificing their rate performance, especially volumetric capacitance at high mass loadings, is a big challenge because of the limited assessable surface area and sluggish electrochemical kinetics of the pseudocapacitive reactions. Here, it is demonstrated that “self‐doping” defects in carbon materials can contribute to additional capacitance with an electrical double‐layer behavior, thus promoting a significant increase in the specific capacitance. As an exemplification, a novel defect‐enriched graphene block with a low specific surface area of 29.7 m² g^?1 and high packing density of 0.917 g cm^?3 performs high gravimetric, volumetric, and areal capacitances of 235 F g^?1, 215 F cm^?3, and 3.95 F cm^?2 (mass loading of 22 mg cm^?2) at 1 A g^?1, respectively, as well as outstanding rate performance. The resulting specific areal capacitance reaches an ultrahigh value of 7.91 F m^?2 including a “self‐doping” defect contribution of 4.81 F m^?2, which is dramatically higher than the theoretical capacitance of graphene (0.21 F m^?2) and most of the reported carbon‐based materials. Therefore, the defect engineering route broadens the avenue to further improve the capacitive performance of carbon materials, especially for compact energy storage under limited surface areas.     

烟草DGAT3基因响应冷胁迫应答的功能研究

二脂酰甘油酰基转移酶（Diacylglycerol acyltransferase,DGAT）是催化三脂酰甘油（TAG）合成途径的关键酶,在植物生长发育和逆境胁迫响应中具有重要的作用。本研究从普通烟草品种K326中克隆得到NtDGAT3基因,利用荧光定量PCR技术分析不同组织中和低温胁迫下NtDGAT3的表达规律。同时,利用CRISPR/Cas9技术制作NtDGAT3敲除植株,对其耐冷性进行了分析。结果表明,NtDGAT3在烟草根、茎、叶中均有表达,且叶部表达量最高;NtDGAT3受冷胁迫强烈诱导,说明该基因可能对冷胁迫有响应。低温处理试验结果表明,敲除突变体ntdgat3对冷敏感,突变体叶片离子渗漏率及丙二醛含量的变化幅度显著高于野生型烟草;在ntdgat3中,膜脂代谢关键基因PLDα1的表达水平显著高于野生型烟草,而PLDδ的表达水平显著低于野生型烟草。以上结果表明,NtDGAT3基因通过PLDα1和PLDδ的表达参与调节植物低温响应。     

固溶处理对SiC_p增强AZ91D镁合金组织及硬度的影响

采用不同固溶温度及保温时间,研究了SiC p增强AZ91D镁合金组织演变及硬度变化行为。结果表明,随固溶温度提高,铸态组织中连续网状β相逐渐消失,汉字状Mg2Si相发生熔断,球化速度加快,400℃时晶界清晰。400℃×16h固溶时,不稳定β相几乎完全固溶至基体中,汉字状Mg2Si球化效果最佳,Al8Mn5相未发生明显变化。400℃×20h固溶后,Mg2Si球化趋势开始减弱,晶粒尺寸出现显著增加。结果表明,β相的消失和Mg2Si相的球化导致合金硬度发生连续下降。400℃×16h后由于固溶强化效果的增加,合金硬度有所提高。     

再入过程中的同位素热源可靠性评估

本文综合考虑微观组织不均匀性等材料的内在分散性,以及载荷历程、工作环境等外在分散性的影响,针对放射性同位素热源（RHU）产品结构特点,选用基于随机有限元法的应力-强度干涉模型,采用解析法与蒙特卡罗法相结合的方式,在有限的试验规模下,定量评价了某型RHU在再入过程中经历一系列环境载荷后的可靠性水平。 利用本文所述方法计算得到：该型RHU在95%置信度下的可靠度置信下限为0.999 989,达到了一般探测器零部件级产品的可靠性评估精度要求,这表明本文所述方法实用、可靠,在RHU的可靠性评估、指导RHU的可靠性设计、降低评估成本方面具有很高的实用价值。     

粉煤灰注浆试验研究

通过对粉煤灰注浆材料的实验研究,不仅确定了最佳配合比,而且从理论上分析了粉煤灰注浆技术的可行性,得出了粉煤灰注浆材料在软土路基路堤中应用具有广阔的发展前景.