Yb∶CaF_(2)透明陶瓷的压力辅助烧结及其性能研究

本文采用化学共沉淀法合成了5%(原子数分数,下同)Yb∶CaF_(2)纳米粉体。经过冷冻干燥后,粉体的团聚程度有所减轻,粉体呈立方片层状,平均颗粒尺寸约为40 nm。以冷冻干燥后的粉体为原料,通过热压烧结结合热等静压(HIP)烧结后处理制备了高光学质量的5%Yb∶CaF_(2)透明陶瓷。分析了热压烧结过程中样品的致密化行为,并对陶瓷的显微结构、直线透过率、吸收光谱及激光性能进行测试与表征。结果表明,陶瓷坯体在热压烧结时的保温阶段存在致密化驱动力的激活阈值,同时HIP后处理能够进一步压缩和排除热压陶瓷内残留气孔,有效提高陶瓷的光学质量。通过热压烧结(625℃×2 h,50 MPa)结合HIP后处理(600℃×3 h,100 MPa Ar)制备的5%Yb∶CaF_(2)透明陶瓷在400和1200 nm处的直线透过率分别为72.6%和92.2%(厚度2 mm),其在976 nm处的吸收截面为0.52×10^(-20)cm^(2)。使用波长为930 nm的光纤耦合二极管激光器(LD)端面泵浦Yb∶CaF_(2)透明陶瓷,获得了最大输出功率为0.81 W、斜率效率为9.7%的准连续激光输出。

不同浓度Y^(3+)离子掺杂对CaF_(2)晶体性能的影响

氟化钙(CaF_(2))晶体具有良好的光学性能和化学稳定性,常常在极端边缘的光学窗口场景中用作基底材料。值得关注的是,CaF_(2)晶体的抗辐照损伤性能作为紫外激光器窗口材料的关键性能之一,由于解理效应导致的损伤增长过快,实际损伤阈值远低于理论值,无法满足紫外大功率激光器件的需求,是限制其在高功率紫外激光器中应用的主要因素。本研究运用材料组分设计,通过掺杂惰性稀土Y^(3+)引入F_(i)^(-),利用Y^(3+)与F_(i)^(-)之间的团簇作用增加解理面之间的键合数,以达到增强层间结合力,降低解理效应,提高损伤阈值的目的。采用坩埚下降法的晶体生长工艺,使用多孔坩埚在同一条件下制备了不同Y^(3+)掺杂浓度的CaF_(2)晶体,并对掺杂的CaF_(2)晶体的光学质量、机械性能以及热学性能进行分析表征。实验结果表明,适量Y^(3+)掺杂对CaF_(2)晶体的光学性能和热学性能,如透过率、热膨胀系数和热导率等改变较小,不影响CaF_(2)晶体的使用;而对机械性能,如剪切强度影响相对突出,当掺杂浓度为原子分数0.36%时,其剪切强度提高了68.4%,对应Y:CaF_(2)晶体的激光损伤阈值提高了166%。

CaF_(2)污泥对硅酸盐水泥性能的影响及机理分析

固废利用是实现“双碳”目标的重要途径之一。本文以固废CaF_(2)污泥为水泥掺合料,通过抗压强度、浆体流动度试验探讨了CaF_(2)污泥掺量对水泥胶凝材料性能的影响,并结合XRD、SEM及TGA-DSC等微观表征测试进行机理分析。结果表明,CaF_(2)污泥的掺加有利于提高水泥胶凝材料的早期强度,CaF_(2)污泥掺量为8%(质量分数)的胶凝材料抗压强度表现较好。CaF_(2)污泥的掺加会导致浆体流动度降低,但掺量低于10%(质量分数)时对浆体流动度影响并不显著,掺量为8%、10%(质量分数)时浆体流动度比未掺加CaF_(2)污泥时降低了3.0%。CaF_(2)污泥在胶凝材料中主要起物理效应,CaF_(2)污泥能够形成更多的结晶位点,促进水泥水化。CaF_(2)污泥掺量增加使水泥的稀释效应及团聚效应显著。掺量为8%(质量分数)的CaF_(2)污泥复合水泥的微观性能较好。

Ni-Mo-Y-CaF_(2)高温自润滑复合材料的制备与摩擦学性能

采用放电等离子烧结(SPS)技术制备了不同CaF_(2)添加量的Ni-Mo-Y-CaF_(2)高温自润滑复合材料,研究了CaF_(2)添加量对复合材料微观结构、力学性能及摩擦磨损性能的影响.结果表明:Ni-Mo-Y-CaF_(2)复合材料的组织均匀致密,复合材料的密度、硬度及屈服强度随CaF_(2)添加量的增加呈下降趋势.温度对复合材料的摩擦磨损性能有显著影响.在室温至800℃,复合材料的平均摩擦系数随温度的增加先降低,在400~600℃略微增加,随后再次降低;平均磨损率随着温度的增加先增加后又降低,400℃时平均磨损率最大.在室温时,Ni-Mo-Y-10CaF_(2)复合材料的平均磨损率最低,约为Ni-Mo-Y合金的1/5;在800℃时,复合材料的磨损率均低于Ni-Mo-Y合金,磨损表面形成致密光滑的润滑膜,润滑膜主要由钼酸钙、钼酸镍及镍和钼的氧化物组成.

Crystal structure,phase transitions,and thermodynamic properties of magnesium metavanadate(MgV_(2)O_(6))

As a promising anode material for magnesium ion rechargeable batteries,magnesium metavanadate(MgV_(2)O_(6))has attracted considerable research interest in recent years.A MgV_(2)O_(6)sample was synthesized via a facile solid-state reaction by multistep-firing stoichiometric mixtures of MgO and V2O5 powder under an air atmosphere.The solid-state phase transition fromα-MgV_(2)O_(6)toβ-MgV_(2)O_(6)occurred at 841 K and the enthalpy change was 4.37±0.04 kJ/mol.The endothermic effect at 1014 K and the enthalpy change was 26.54±0.26 kJ/mol,which is related to the incongruent melting ofβ-MgV_(2)O_(6).In situ XRD was performed to investigate phase transition of the as-prepared MgV_(2)O_(6)at high temperatures.The cell parameters obtained by Rietveld refinement indicated that it crystallizes in a monoclinic system with the C2/m space group,and the lattice parameters of a=9.280 A°,b=3.501 A°,c=6.731 A°,β=111.76°.The solid-state phase transition fromα-MgV_(2)O_(6)toβ-MgV_(2)O_(6)was further studied by thermal kinetics,indicating that this process is controlled first by a fibril-like mechanism and then by a spherulitic-type mechanism with an increasing heating rate.Additionally,the enthalpy change of MgV_(2)O_(6)at high temperatures was measured utilizing the drop calorimetry,heat capacity was calculated and given as:Cp=208.3+0.03583T-4809000T^(−2)(298-923 K)(J mol^(−1)K^(−1)),the high-temperature heat capacity can be used to calculate Gibbs free energy of MgV_(2)O_(6)at high temperatures.

Y^(3+)∶CaF_(2)透明陶瓷的制备及其显微结构研究

采用化学沉淀法合成Y^(3+)∶CaF_(2)粉体,用真空热压烧结技术制备透明陶瓷。通过XRD、SEM与TEM分析粉体特性,并研究Y^(3+)∶CaF_(2)透明陶瓷显微结构与透过率的关系。结果表明,Y^(3+)∶CaF_(2)粉体为立方萤石相晶体结构。随Y^(3+)掺杂量的增加,粉体的平均粒径尺寸逐渐减小,晶胞参数由5.4521增大到5.4655;在900℃下烧结3 h得到的5%Y^(3+)掺杂的CaF_(2)陶瓷透过率最高,样品在500和1500 nm处的透过率分别为73.1%和86.4%。改变Y^(3+)掺杂量与烧结温度均可调控陶瓷的显微结构。晶粒生长速率低,气孔不易排出,速率过高,气孔易被包裹在晶粒内部,两种情况均会降低陶瓷的透过率。本研究工作为制备高品质复合结构CaF_(2)透明陶瓷提供了参考。

Preparation and Spectral Properties of Er,Na∶CaF_(2) Transparent Ceramics

Er^(3+),Na^(+)co-doped CaF_(2) transparent ceramics with Er^(3+)dopant concentration of 3% and Na^(+) of 0%,0.5%,1.0%,1.5% and 2.0% were fabricated by the vacuum hot pressing method with 16 mm in diameter and 3 mm in thickness.The average grain size of the obtained Er,Na∶CaF_(2) powders varied from 28 nm to 36 nm with the shape of sphere.The effects of Na^(+) doping on the transmittance,microstructure and spectral properties of Er^(3+)∶CaF_(2) transparent ceramics were investigated.The transmittance of all the obtained ceramic samples is above 84%in the wavelength of 1000 nm.The results show that after introducing Na^(+)into Er^(3+)∶CaF_(2) transparent ceramics,charge-neutralized Er^(3+)-Na^(+) structure formed which prevent Er^(3+) from clustering.The emission spectra of Er^(3+) in CaF_(2) transparent ceramics at around 1.5 and 2.7μm could be modulated by adjusting the concentration of Na^(+) and the near-infrared fluorescence lifetime at around 1.5μm increase with the increasing of Na^(+) concentration,reaching a maximum of 56.75 ms.

Sensing the heavy water concentration in an H_(2)O-D_(2)O mixture by solid-solid phononic crystals

A new method based on phononic crystals is presented to detect the concentration of heavy water(D_(2)O)in an H_(2)O-D_(2)O mixture.Results have been obtained and analyzed in the concentration range of 0%-10%and 90%-100%D_(2)O.A proposed structure of tungsten scatterers in an aluminum host is studied.In order to detect the target material,a cavity region is considered as a sound wave resonator in which the target material with different concentrations of D_(2)O is embedded.By changing the concentration of D_(2)O in the H_(2)O-D_(2)O mixture,the resonance frequency undergoes a frequency shift.Each 1%change in D_(2)O concentration in the H_(2)O-D_(2)O mixture causes a frequency change of about 120 Hz.The finite element method is used as the numerical method to calculate and analyze the natural frequencies and transmission spectra of the proposed sensor.The performance evaluation index shows a high Q factor up to 1475758 and a high sensitivity up to 13075,which are acceptable values for sensing purposes.The other figures of merit related to the detection performance also indicate high-quality performance of the designed sensor.

Crystallization management of CsPbI_(2)Br perovskites by PbAc_(2)-incorporated twice spin-coating process for efficient and stable CsPbI_(2)Br perovskite solar cells

CsPbI_(2)Br perovskite solar cell has been extensively studied due to its exceptional thermal stability and relatively stable perovskite phase structure.However,the presence of bromine leads to a rapid crystallization rate of CsPbI_(2)Br films,resulting in small grain size and high defect density.Additionally,CsPbI_(2)Br demonstrates poor light absorption due to its wide bandgap.Therefore,it is crucial to control the crystallization rate and increase the film thickness to reduce defect density,enhance light absorption,and improve photovoltaic performance.In this study,we utilized a PbAc_(2)-incorporated twice spincoating(PTS) process to address these issues.Initially,PbAc_(2) was added to the CsPbI_(2)Br precursor solution to form a CsPbI_(2)Br film,which was then coated with the CsPbI_(2)Br precursor solution to produce the PTS film,Ac^(-)can delay the perovskite crystallization,leading to the formation of thicker and denser CsPbI_(2)Br films.Moreover,lone-pair electrons of the oxygen atom provided by Ac^(-)formed coordination bonds with under-coordinated Pb~(2+) ions to fill halogen ion vacancies,thereby reducing the defect density.Ultimately,the PTS CsPbI_(2)Br device achieved a peak power conversion efficiency(PCE) of 16.19% and maintained 96.7% of its initial PCE over 1500 h at room temperature under 25% relative humidity without any encapsulation.

Regulating crystal phase of TiO_(2) to enhance catalytic activity of Ni/TiO_(2) for solar-driven dry reforming of methane

Ni/TiO_(2) catalyst is widely employed for photo-driven DRM reaction while the influence of crystal structure of TiO_(2) remains unclear.In this work,the rutile/anatase ratio in supports was successfully controlled by varying the calcination temperature of anatase-TiO_(2).Structural characterizations revealed that a distinct TiO_(x) coating on the Ni nanoparticles(NPs)was evident for Ni/TiO_(2)-700 catalyst due to strong metal-support interaction.It is observed that the TiOx overlayer gradually disappeared as the ratio of rutile/anatase increased,thereby enhancing the exposure of Ni active sites.The exposed Ni sites enhanced visible light absorption and boosted the dissociation capability of CH4,which led to the much elevated catalytic activity for Ni/TiO_(2)-950 in which rutile dominated.Therefore,the catalytic activity of solar-driven DRM reaction was significantly influenced by the rutile/anatase ratio.Ni/TiO_(2)-950,characterized by a predominant rutile phase,exhibited the highest DRM reactivity,with remarkable H_(2) and CO production rates reaching as high as 87.4 and 220.2 mmol/(g·h),respectively.These rates were approximately 257 and 130 times higher,respectively,compared to those obtained on Ni/TiO_(2)-700 with anatase.This study suggests that the optimization of crystal structure of TiO_(2) support can effectively enhance the performance of photothermal DRM reaction.

Localization effect in single crystal of RuAs_(2)

We report the magnetotransport and thermal properties of RuAs_(2) single crystal.RuAs_(2) exhibits semiconductor behavior and localization effect.The crossover from normal state to diffusive transport in the weak localization(WL)state and then to variable range hopping(VRH)transport in the strong localization state has been observed.The transitions can be reflected in the measurement of resistivity and Seebeck coefficient.Negative magnetoresistance(NMR)emerges with the appearance of localization effect and is gradually suppressed in high magnetic field.The temperature dependent phase coherence length extracted from the fittings of NMR also indicates the transition from WL to VRH.The measurement of Hall effect reveals an anomaly of temperature dependent carrier concentration caused by localization effect.Our findings show that RuAs_(2) is a suitable platform to study the localized state.

CaCl_(2)-CaF_(2)-CaO三元体系的相图计算

基于Calphad方法,首先对CaCl_(2)-CaO、CaCl_(2)-CaF_(2)和CaO-CaF_(2)体系进行了系统的热力学评估和优化。采用置换溶液模型来描述液相和固溶体相的吉布斯自由能,所有中间相因其固溶区域十分有限而近似处理成准化学计量比化合物,且其自由能依据Neumann-Kopp规则定义。其次,利用Muggianu溶液几何模型将优化获得的所有子二元系的模型参数扩展至CaCl_(2)-CaO-CaF_(2)三元体系。最后,对共晶点进行配样和差示扫描量热法(DSC)测试,通过引入三元交互参数使计算结果与试验数据一致,从而获得了一套自洽的CaCl_(2)-CaO-CaF_(2)三元体系热力学数据库。

激光照明用YAG∶Ce-CaF_(2)荧光陶瓷的冷烧结制备

荧光陶瓷是激光照明的关键材料。为探究低温制备荧光陶瓷的可行性,采用冷烧结工艺在425℃成功制备了致密度高、晶粒尺寸均匀、相界分明的YAG∶Ce-CaF_(2)复合荧光陶瓷。结果表明:发光相与基体之间没有可检测到的界面反应;制备的荧光陶瓷具有较高的量子效率(74.3%)、较好的热导率(室温可达9.4 W·m^(-1)·K^(-1))、优异的热稳定性(在400 K时发光强度仅损失4.3%);在蓝光激光(451 nm)激发下,复合荧光陶瓷表现出良好的黄光发射,并展现出光通量为910.7 lm和流明效率为91.07 lm·W^(-1)的高亮度白色激光照明,其荧光寿命无衰减(66 ns),相关色温为4483~8247 K,显色指数为73.4~83.6。冷烧结工艺是低温条件下制备性能优良荧光陶瓷的新方法。

Crystal growth,spectral properties and Judd-Ofelt analysis of Pr:CaF_(2)-YF_(3)

The 0.6 at.%Pr^(3+)-doped CaF_(2)-YF_(3)crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure.The absorption spectrum,emission spectrum,Judd-Ofelt analysis and fluorescence decay curve at room temperature were discussed.The fluorescence lifetime of Pr:CaF_(2)-YF_(3)crystal was 45.46µs,and theσem·τof ^(3)P0→^(3)H_(6) and ^(3)P0→^(3)F_(2) transitions were calculated to be 80.92×10^(−20) cm^(2)·µs and 388.7×10^(−20) cm^(2)·µs,respectively.The FWHMs are 20.1 nm and 6.8 nm,which are higher than those of Pr:LiYF_(4),Pr:LiLuF_(4),Pr:LiGdF_(4) and Pr:BaY_(2)F_(8) crystals.The results show that the Pr:CaF_(2)-YF_(3)crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.

CaF_2单晶体应用研究

氟化钙晶体具有良好的光学性能、机械性能及物化稳定性 ,有透光范围宽广 ( 0 .1 2 5～1 0 μm)、透过率高 ,折射率低 ,相对色散大等优点。自真空紫外至中红外波段被广泛地用作窗口、透镜、棱镜、分束器、基板等材料。高纯度的CaF2 单晶体是真空紫外波段准分子激光器良好的窗口材料 ,单晶或热锻单晶CaF2 材料是一氧化碳及化学激光器的窗口材料。大尺寸、完整性好的CaF2 晶体更是紫外与可见波段优秀的镜头材料。CaF2 晶体亦可作为激光晶体和无机闪烁晶体材料。迄今为止 ,碱土氟化物晶体真空紫外波段的良好透光性能是其它材料无法相比的。此外 ,用于真空紫外波段的CaF2 单晶材料还具有抗辐射、臭氧阻高、损伤阈值高、抗氟气腐蚀和成本低的优点。近期研究表明 ,CaF2 晶体真空紫外波段主要性能已达到MgF2 晶体同等水平。在紫外和可见波段 ,CaF2 晶体由于特殊的折射指数与相对色散值 ,使其成为复消色差透镜理想的光学材料。晶体完整性好 ,光学均匀性好于 1 0 -5 ,应力双折射通常在 5～ 1 5nm/cm范围内。用于高倍显微镜镜头的CaF2 只有几个毫米大小 ,而用于侦察、天文、紫外光刻的CaF2晶体 ,其直径最大已接近 30 0mm。长春光机所的CaF2 晶体已被用于这些方面 ,最大镜头尺寸1 90mm。人工CaF2

Effect of Fe_2O_3 on non-isothermal crystallization of CaO-MgO-Al_2O_3-SiO_2 glass

The crystallization behavior and kinetics of CaO-MgO-Al2O3 SiO2（CMAS） glass with the Fe2O3 content ranging from zero to 5%were investigated by differential scanning calorimetry（DSC）.The structure and phase analyses were made by Fourier transform infrared spectroscopy（FT-IR） and X-ray diffraction（XRD）.The experiment results show that the endothermic peak temperature about 760℃ is associated with transition and the exothermic peak temperature about 1000℃ is associated with crystallization.The crystallization peak temperature decreases with increasing the Fe203 content.The crystallization mechanism is changed from two-dimensional crystallization to one-dimensional growth,and the intensity of diopside peaks becomes stronger gradually.There is a saltation for the crystallization temperature with the addition of 0.5%Fe2O3 due to the decomposition of Fe2O3.Si-O-Si,O-Si-O and T-O-T（T=Si,Fe,Al） linkages are observed in Fe2O3-CaO-MgO-Al2O3-SiO2 glass.

直径200毫米CaF_2单晶体生长

我们采用一种特定设计的Bridgman Stockbarger炉 ,已经稳定地生长出直径 2 0 0mm ,高1 70mm的CaF2 晶体 ,晶体初端与终端有时出现较明显的光散射、亮点及包裹体。晶体初始端主要缺陷是零星分布散射亮点 ,而散射光柱则很轻 ;晶体终端出现 30mm左右的指向终端逐渐变重的散射光柱。进一步试验表明 ,通过改进工艺 ,端部效应影响可以得到有效地改进。大尺寸CaF2 单晶体生长工艺技术的成熟主要表现在晶体结构完整性好 ,其次是低角度晶界处的光学连续性好。大尺寸单晶体的制做中 ,结构完整性无论对晶体光学性能还是对元件制做都是至关重要的。决定结构完整性的关键因素是炉内温场分布 ,其次是工艺参数的选取及合理匹配。在低角度晶界界面上 ,应该不存在杂质沉积或者说杂质沉积甚微 ,无微气泡层出现。界面光学连续性好 ,光波通过此处无明显的波前畸变发生。结构完整性好的晶体 ,通过精密退火 ,应力可达到 5～ 8nm/cm ,保证各种光学元件的加工制做及材料性能的要求。目前这些晶体已经进入国内外市场 ,被加工成1 90mm、1 5 7mm以及98mm光学透镜及窗口。

CaO-SiO_2-Na_2O-CaF_2-Al_2O_3-MgO渣系的粘度和结晶温度

采用CaO SiO2 Na2 O CaF2 Al2 O3 MgO渣系 ,用差热分析仪测定熔渣的结晶温度 ,用粘度测定仪测定熔渣的粘度 ,研究结晶温度和粘度与碱度、w (Na2 CO3 )、w (CaF2 )、w (Al2 O3 )和w(MgO)之间的关系 ,并得到相应的回归方程·利用这两个回归方程 ,可以预测连铸保护渣的结晶性能和粘性特征·化学成分通过改变粘度 ,来影响晶核形成速度和晶体成长速度 。

CaF_(2):Eu^(2+)纳米粉体的水热合成及发光性能研究

针对高生物毒性氚化水的检测需求,无机纳米闪烁体提供了一种新的解决思路。采用水热法合成了CaF_(2):Eu^(2+)纳米颗粒,结合XRD、SEM、FS等表征手段,对比了水热反应条件对粉体物相组成、微观形貌、光学性能的影响。结果表明,所获样品均为立方结构的纯相CaF_(2),近球形颗粒分散良好,平均粒径约30 nm。CaF_(2):Eu^(2+)纳米粉体在339 nm紫外光激发下显示出425 nm的特征发射峰,在180℃、24 h条件下具有最佳的发射强度。

B_2O_3替代CaF_2铁水预处理脱磷的热力学研究

通过MoSi管式高温炉在1450℃下研究了用0～8%B_2O_3替代40%CaO-52%Fe_2O_3铁水预处理渣中0～8%CaF_2的含量,对初始硅含量为0.61%,初始磷含量0.06%～0.09%的铁水脱磷效果。实验结果表明,B_2O_3替换CaF_2后,预处理脱磷渣氧化性增加,铁水的脱磷率大于80%,渣的磷容量略有降低,从9.35×10^(21)变化到7.48×10^(21),可以满足预处理脱磷的要求。