电流驰豫法测试氧化镧掺杂的氧化铈中氧离子迁移

采用甘氨酸-硝酸盐法(GNP)合成了Ce0.65La0.35O1.825(LDC)粉末,在1400℃下烧结10 h得到陶瓷试样,用XRD和SEM表征了样品的物相和表面形貌。用直流电场测试了试样在不同温度下的电流驰豫现象,并计算了不同温度下试样中迁移氧离子数目和材料直流电导率。结果表明,在固态电解质材料中突然施加强电场,可迁移离子基本都发生了位置偏移,但极少部分可以产生长程迁移。随着温度的升高,样品中发生迁移的氧离子数目增加,但都远小于氧空位总量。迁移氧离子数目与温度之间满足阿累尼乌斯公式,其迁移活化能为0.83 eV。     

Ti-62A合金热变形过程中的流变应力特性及组织演变

通过 Gleeble-3800 热模拟试验机的热压缩实验，研究了 Ti-62A 合金在 800、850、900 和 950℃，应变速率为 0.001、0.01、0.1 和 1s-1 下的热变形行为和动态再结晶（DRX）规律。结果表明：Ti-62A 合金的流变应力受应变速率和变形温度的影响显著；流变应力随着变形温度的升高和应变速率的降低而降低；在 900~950℃、应变速率 0.01~1s-1 条件下，Ti-62A 合金的热变形应力-应变曲线属于动态回复型；该合金的热变形机制主要由位错运动控制，其动态软化机制包括晶界滑动和位错对消、攀移机制；Ti-62A 合金在热变形过程中，动态再结晶更有可能发生在较高的温度和较低的应变速率下，即 950℃ 和 0.001s-1；基于经典位错密度理论和 DRX 动力学理论，建立了加工硬化—动态回复和 DRX 软化效应的两阶段本构模型。DEFORM-3D 软件的仿真模拟结果证实，基于 DRX 软化效应的本构模型对 Ti-62A 合金在动态再结晶阶段的热变形行为的预测具有较高的准确性，能够为实际生产工艺的制定提供技术参考。     

核燃料用γ-U合金的成分规律

铀合金作为一种重要核燃料,其体心立方结构的高温稳定的γ-U合金具有较好的综合性能,是合金设计所追求的目标。本文引入描述稳定固溶体结构的"团簇加连接原子"模型,用于建立γ-U固溶体合金的结构模型和相应成分式,指出其结构单元为体心立方第一近邻配位多面体团簇加3个连接原子构成。进而利用该结构单元对现有合金成分进行了解析,能够稳定形成体心立方bcc结构的合金均满足上述模型,如[Mo-U14]Mo3(U-10.7Mo),[Zr-U14]Nb3(U-7.5Nb-2.5Zr,即不锈铀)等,这些合金实际上均在各自体系中具有最优良的结构稳定性,显示出优异的耐蚀性。本文证实,基于团簇加连接原子模型的成分设计方法在预测γ-U合金成分与性能上具有重要指导价值。     

热稳定处理时间对TNM合金糊状区组织的影响

利用真空非自耗电弧炉制备了TNM(Ti-44Al-4Nb-1Mo-0.1B at.%)合金锭,研究其铸态组织形貌,并利用Bridgeman定向凝固装置对TNM合金进行热稳定处理实验,分析热稳定处理时间对合金定向凝固糊状区的影响。实验结果显示,其铸态组织是以(α₂+γ)片层团为主体,网络状B2相、细小的γ相及硼化物分布于片层团间的近片层组织。热稳定处理时,热稳定时间越长、TNM合金固/液界面越平整,界面前沿温度场和溶质场趋向均匀,但从减少坩埚对熔体的污染的角度考虑,热稳定处理时间不宜过长,30~60 min的热稳定时间即可提供平整的定向凝固启动界面。 热稳定处理影响着TNM合金固/液界面附近固液两相中Al元素的分布,进而影响硼化物的分布。     

铸态Mg-8Y-6Gd-1Nd-0.17Zn稀土镁合金高温压缩本构行为及加工图

研究了铸态Mg-8Y-6Gd-1Nd-0.17Zn镁合金在应变量为50%、温度350℃~450℃、应变速率0.0001s-1~0.1s-1的范围内热压缩过程中的本构行为、组织演变和热加工性能。通过选用双曲正弦本构方程来描述合金的流变行为以及变形参数间的关系。实验结果表明，温度和应变速率对Mg-8Y-6Gd-1Nd-0.17Zn镁合金的流变应力行为有重要影响，其流变应力随温度的降低和应变速率的增加而增大，并且在温度高于400℃压缩时，合金的真应力应变曲线具有典型的动态再结晶特性。在本实验条件下，该合金变形期间的活化能（Q）和应力指数（n）分别为359.258 KJ / mol 和5.24，实验值与计算值之间的平均误差（ARE）为3.37％。最后基于动态材料模型加工理论，结合热加工图和压缩过程中的组织演变，确定了该合金的最佳热加工参数为：加热温度400~450℃，应变速率为0.0001s-1~0.001s-1。     

Site occupancy and enhanced luminescence of broadband NIR gallogermanate phosphors by energy transfer

Super broadband near-infrared (NIR) La₃Ga₅GeO₁₄(LGGO): Cr³⁺ phosphor is in urgent needs for food testing. Unfortunately, it suffers from poor luminescence intensity in applications. Herein, the enhanced NIR luminescence performance can be realized in LGGO: Pr³⁺, Cr³⁺. The preferential crystallographic site of Cr³⁺ is validated on the basis of EPR spectrum, Rietveld refinement, and the first-principles DFT calculations. It is of great importance that the as-prepared phosphors can be excited by blue light (460 nm), which is beneficial to the application of blue-pumped LEDs. The critical distance of Pr³⁺ in LGGO host has been calculated by concentration-quenching method. For co-doped sample, it is observed that Cr³⁺ luminescence intensity enhancement by a factor of 3 can be achieved by doping Pr³⁺ owing to the energy transfer from Pr³⁺ to Cr³⁺. In addition, the introduction of Pr³⁺ can also improve the Cr³⁺ luminescence intensity at elevated temperature. Furthermore, using the optimized phosphor, a blue-based NIR phosphor-converted LEDs (NIR pc- LEDs) is fabricated, the forward voltage and the intensity of LED hardly change after thermal aging for 500 hours under high temperature/ high humidity condition, indicating its great reliability for NIR pc-LEDs. Therefore, LGGO:Pr³⁺, Cr³⁺ has great potential to serve as an attractive candidate in the application of blue light-excited NIR pc-LEDs in view of its capability for blue to enhanced broadband NIR conversion.     

Facile synthesis of the desired red phosphor Li2Ca2Mg2Si2N6:Eu2+ for high CRI white LEDs and plant growth LED device

The red emission with suitable peak wavelength and narrow band is acutely required for high color rendering index (CRI) white LEDs without at the cost of the luminous efficacy. Herein, the Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ red phosphor was prepared with facile solid-state method using Ca₃N₂, Mg₃N₂, Si₃N₄, Li₃N, and Eu₂O₃ as the safety raw materials under atmospheric pressure for the first time, which shows red emission peaking at 638 nm with full width at half maximum (FWHM) of 62 nm under blue light irradiation and becomes the desired red phosphor to realize the balance between luminous efficacy and high CRI in white LEDs. The morphology, structure, luminescence properties, thermal quenching behavior, and chromaticity stability of the Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ phosphor are investigated in detail. Concentration quenching occurs when the Eu²⁺ content exceeds 1.0 mol%, whereas high-temperature photoluminescent measurements show a 32% drop from the room-temperature efficiency at 423 K. In view of the excellent luminescence performances of Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ phosphor, a white LEDs with CRI of 91 as a proof-of-concept experiment was fabricated by coating the title phosphor with Y₃Al₅O₁₂:Ce³⁺ on a blue LED chip. In addition, the potential application of the title phosphor in plant growth LED device was also demonstrated. All the results indicate that Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ is a promising red-emitting phosphor for blue LED-based high CRI white LEDs and plant growth lighting sources.     

Indentation cracking and deformation mechanism of sodium aluminoborosilicate glasses

Developing less brittle oxide glasses is a grand challenge in the field of glass science and technology, as it would pave the way toward new glass applications and limit the overall raw material usage and energy consumption. However, in order to achieve this goal, more insight into the correlation between the chemical composition and material properties is required. In this work, we focus on the mechanical properties of quaternary sodium aluminoborosilicate glasses, wherein systematic changes in glass chemistry yield different resistances to indentation crack initiation. We discuss the origin of the composition dependence of indentation cracking based on an evaluation of the deformation mechanism taking place during the indentation event. To this end, we use a simple metric, the extent of indent side length recovery upon annealing, to quantify the extent of reversible volume deformation. Finally, we also compare the compositional trend in crack initiation resistance to that in crack growth resistance (fracture toughness), showing no simple correlation among the two.     

Experimental investigation of high-temperature corrosion properties in simulated reducing-sulphidizing atmospheres of the waterwall fireside in the boiler

The presence of reducing atmospheres of the waterwall fireside in the boiler due to extensive use of low-NOx combustion mode caused severe high-temperature corrosion problems. In this study, high-temperature sulphur corrosion properties of two types of low alloyed waterwall steel (15CrMoG and 12Cr1MoVG) in two kinds of reducing-sulphidizing atmospheres were investigated by lab-scale experiments. The experimental atmospheres and temperature were simulated according to field measurements in the boiler of a thermal power plant. The experimental results showed that the reducing-sulphidizing atmosphere with CO was more corrosive, and the CO accelerated the corrosion of H₂S and worsened the corrosion. The CO inhibited the formation of oxide scales, provided some corrosion resistance, and produced the intensely corrosive COS. The corrosivity of the alkali metal chlorides was limited in the reducing-sulphidizing atmosphere without CO, while the corrosion was strongly hindered in the reducing-sulphidizing atmosphere with CO.