油溶性LaF_(3)纳米微粒与齿轮油典型添加剂的配伍性能及其应用研究

采用二(2-乙基己基)磷酸(D2EHPA)为修饰剂制备了油溶性LaF_(3)纳米微粒,使用四球摩擦磨损试验机探究了其与齿轮油典型添加剂复配后的摩擦学性能,将其作为添加剂应用到市售重负荷工业齿轮油中,考察了其在齿轮油中的应用效果。结果表明:所制备的油溶性LaF_(3)纳米微粒与硫化烯烃(T321)、硫代磷酸复酯胺盐(T307)和丁基异辛基磷酸十二胺盐(T308B)等典型的添加剂具有良好的协同效应;LaF_(3)纳米微粒加入到重负荷工业齿轮油中,不仅能够增强齿轮油的减摩和抗磨性能,而且还能提高油品的承载能力。

多坩埚温度梯度法生长Dy^(3+)∶LaF_(3)晶体及发光特性

采用多坩埚温度梯度法(Multi-crucible temperature gradient technology,MC-TGT)制备了Dy^(3+)掺杂氟化镧(Dy^(3+)∶LaF_(3))晶体。通过电感耦合等离子体发射光谱仪、透射光谱、吸收光谱、荧光光谱等手段对Dy^(3+)在LaF_(3)晶体中的实际掺杂浓度、中红外透过光谱、可见光波段光谱特性等进行了研究。实验结果表明,Dy^(3+)在LaF_(3)晶体中的分凝系数约为0.8;格位浓度随着Dy^(3+)掺杂浓度提高而增加,2%Dy∶LaF_(3)晶体中的格位浓度达5.90×10^(20)ions·cm^(-3)。在1%Dy∶LaF_(3)晶体中,采用400 nm光激发,发光中心波长位于601 nm的发射谱带强度最大,位于511 nm的发射峰最宽,半高宽达152 nm;改用450 nm光激发,最强发射峰移至677 nm,最宽发射峰位于568 nm处。提高Dy^(3+)掺杂浓度到2%,采用400 nm或450 nm光激发,发光中心波长均位于478 nm和571 nm。在透射光谱2.5~9μm范围内,Dy∶LaF_(3)晶体(厚度为0.96 mm)红外波段透过率达85%以上。Dy∶LaF_(3)晶体有望在可见光、中红外等激光领域得到应用。

0-水热合成Sr^_(2)LaF_(7):RE^(3+)(RE=Ce,Tb,Dy,Ce-Tb,Ce-Dy)荧光材料

采用水热合成法在没有添加剂的情况下成功合成了Sr^_(2)LaF_(7):RE^(3+)(RE=Ce,Tb,Dy,Ce-Tb,Ce-Dy)下转换荧光粉。采用X射线衍射(XRD)表征了样品的晶体结构,用扫描电子显微镜(SEM)表征了样品的形貌特征,获得了形态不规则的纳米级Sr^_(2)LaF_(7)晶体。为进一步研究其下转换发光,采用傅里叶F-7000分光光度计得到样品的发射光谱和激发光谱。用光谱详细地证明了Sr^_(2)LaF_(7)中Ce^(3+)-Tb^(3+)、Ce^(3+)-Dy^(3+)之间的能量转移。找到了Ce^(3+)的最佳浓度,调节了Tb^(3+)掺杂的浓度,因为能量转移的作用,得到的发光颜色发生了由蓝到绿的变化。综上所述,获得了不同发射颜色的发光材料,这些材料有望在未来的固态发光显示领域得到应用。

X-RAY DIFFRACTION ANALYSIS OF MOLTEN LaF_(3)-XF(X = Li, K)

The radial distribution functions of molten salt solution LaF_(3)-4LiF and LaF_(3)-4KF systems were derived from X-ray difraction data at 1,083 K.The interionic distances in the melts were obtained,e.g.La^(3+)-F^(-)interaction was 0.238 and 0.233nm respectively in molten LaF_(3)-4LiF and LaF_(3)-4KF systems.The temperature and coulombic force of La^(3+)were discussed concerning the results of interionic distances in melt.

LaF_(3):Eu纳米晶的水热合成及荧光特性

采用水热法合成了不同Eu^(3+)掺杂质量比的LaF_(3)∶Eu纳米晶,研究了样品的晶体结构、形貌和荧光性能.XRD数据分析表明,水热反应温度升高利于LaF_(3)晶体结构的形成,140℃下晶体结构趋于完善.随着Eu^(3+)掺杂质量比增大其衍射峰的位置向较大θ角方向发生了一定程度的偏移,说明掺杂Eu^(3+)与基质晶格中的La^(3+)发生部分的同晶取代.SEM分析表明,样品为30~50 nm左右的微球,形貌均一.荧光分析表明,LaF_(3)∶Eu粉末的荧光效果在Eu^(3+)掺杂质量比为0.04、反应温度为140℃、反应时间为10 h时达到最佳.

Sensing properties and mechanisms of LaF_(3)-Co_(3)O_(4) nanorods for low-concentration methanol detection

Methanol is one of the characteristic gases that distinguish between healthy individuals and lung cancer(LC)lesions in exhaled human breath.Its concentration in exhaled breath is generally below one part per million(1×10^(-6)).The second-phase composite is widely regarded as one of the methods to improve the gas-sensing perfor-mance of metal oxide semiconductor(MOS)materials.In this study,LaF_(3)-Co_(3)O_(4) was synthesized by a simple hydrothermal method to enhance its low-concentration methanol gas-sensing performance.5 at%LaF_(3)-Co_(3)O_(4) nanorods exhibited excellent methanol detection performance,including a wider linear detection concentration range(0.2×10^(-6)~5×10^(-6)),a response value exceeding 4.0 for 1×10^(-6)methanol at 275°C and 75%relative humidity(RH),long-term stability(maximum deviation within 15%over 2 weeks),and excellent selectivity.The mechanism of performance enhancement was studied using various techniques,and density functional theory.The special spinel structure of Co_(3)O_(4),the high ionic migration of F-in LaF_(3),the larger specific surface area of 5 at%LaF_(3)-Co_(3)O_(4) nanorods,and the generated crystal defects all explain the excellentmethanol gas-sensing property.This work provides a novel route to prepare MOS composite materials for low-concentration methanol gas detection.

La_(2)O_(3)在LaF_(3)-LiF熔盐体系的溶解度研究

La_(2)O_(3)溶解度对熔盐电解制备金属La及其合金有重要影响。利用等温饱和法考察了LaF_(3)含量、温度对La_(2)O_(3)在LaF_(3)-LiF熔盐体系中溶解度的影响,并采用最小二乘法对数据进行了分析,建立了LaF_(3)含量、温度与La_(2)O_(3)溶解度之间的数学回归方程。研究结果表明:La_(2)O_(3)溶解度与温度、LaF_(3)含量均为正向性线性关系,随温度的升高而线性增大;在合适的温度下,随熔盐中LaF_(3)含量的升高而线性增大;La_(2)O_(3)溶解度(S)与温度(t)、LaF_(3)含量(ω)的关系可以表示为:S=1×10^(-4)ω·t-0.085ω-0.003t+3.60(ω≤75%),通过此方程计算不同温度、体系下La_(2)O_(3)溶解度,对电解法生产金属La有一定指导意义。

Strategy to boost hydrolysis resistance and stabilize low infrared emissivity of ZrB_(2) via nanoscale LaF_(3) surface modification

Owing to its excellent high-temperature resistance and high conductivity,zirconium diboride(ZrB_(2)) has been applied as an infrared suppression coating.However,ZrB_(2)is susceptible to hydrolysis under high-moisture conditions and even under mild working temperatures.The improvement in the hydrophobicity of the ZrB_(2)surface effectively reduces wetting by water and suppresses hydrolysis reaction,particularly under high-temperature and high-moisture conditions.Herein,we report a novel,easy,and highly reproducible method for producing a fully coated ZrB_(2)surface by developing a nanoscale hydrophobic layer of glassy LaF_(3)on the surface of ZrB_(2)powder particles in situ(i.e.,during the carbothermal synthesis of ZrB_(2)).Through the tests carried out at 200 ℃for 100-300 h in a hydrothermal reactor,the produced powders displayed remarkably high long-term hydrolysis resistance and pronounced chemical stability.Compared with treated ZrB_(2),ZrB_(2)@LaF_(3)remained lower infrared emissivity when continuously intensifying hydrolyzation process.The results suggest that a nanoscale surface modification strategy can be applied to stabilize the infrared emissivity of ZrB_(2)in a water-oxygen coupling environment.

Enhancement of solar-driven photocatalytic activity of oxygen vacancy-rich Bi/BiOBr/Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)composites through synergetic strategy of upconversion function and plasmonic effect

For better use of solar energy,the development of efficient broadband photocatalyst has attracted extraordinary attention.In this study,a ternary composite consisting of Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)upconversion(UC)nanocrystals and Bi nanoparticles loaded BiOBr nanosheets with oxygen vacancies(OVs,SLFBB)was designed and synthesized by multi-step solvent-thermal method.Mechanisms of in-situ formation of Bi nanoparticles and OVs in BiOBr/Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)composites(SFLB)are clarified.The Bi metal and OVs enhanced the light-harvesting capacity in the region of visible-near-infrared(Vis-NIR),and promoted the separation of electron-hole(e-/h+)pairs.Furthermore,the surface plasmon resonance(SPR)effect of Bi metal can improve the energy transfer from Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)to BiOBr via nonradiative energy transfer process,resulting in enhancing the light utilization from up-converting NIR into Vis light.Due to the synergistic effects of UC function,SPR and OVs,the SFLBB exhibited obviously enhanced photocatalytic ability for the degradation of BPA with a rate of 8.9×10^(-3) min^(-1),which is about 2.78 times higher than 3.2×10^(-3) min^(-1) of BiOBr(BOB)under UV-Vis-NIR light irradiation.This work provides a novel strategy for the project of high-efficiency Bismuth-based broadband photocatalysts,which is helpful to fur-ther understand the mechanism of enhanced photocatalysis by UC function and plasmonic effect.